add a more verbose description of operators (#7263)

# Description

I was thinking that it may be helpful to have a more verbose description
of our operators. Please let me know if you have better wording.

Also, while not strictly considered an operator, i added `not` to avoid
some confusion.
<img width="1574" alt="Screenshot 2022-11-28 at 7 57 30 PM"
src="https://user-images.githubusercontent.com/343840/204419666-7c4dbb43-26f5-4cd5-9a4e-a1555a9e700f.png">


# User-Facing Changes

Adds description column

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-command/src/core_commands/help_operators.rs

@@ -40,6 +40,8 @@ impl Command for HelpOperators {
             vals.push(Value::string(op.operator, head));
             cols.push("name".into());
             vals.push(Value::string(op.name, head));
+            cols.push("description".into());
+            vals.push(Value::string(op.description, head));
             cols.push("precedence".into());
             vals.push(Value::int(op.precedence, head));
             recs.push(Value::Record {
@@ -59,6 +61,7 @@ struct OperatorInfo {
     op_type: String,
     operator: String,
     name: String,
+    description: String,
     precedence: i64,
 }
 
@@ -68,210 +71,252 @@ fn generate_operator_info() -> Vec<OperatorInfo> {
             op_type: "Assignment".into(),
             operator: "=".into(),
             name: "Assign".into(),
+            description: "Assigns a value to a variable.".into(),
             precedence: 10,
         },
         OperatorInfo {
             op_type: "Assignment".into(),
             operator: "+=".into(),
             name: "PlusAssign".into(),
+            description: "Adds a value to a variable.".into(),
             precedence: 10,
         },
         OperatorInfo {
             op_type: "Assignment".into(),
             operator: "-=".into(),
             name: "MinusAssign".into(),
+            description: "Subtracts a value from a variable.".into(),
             precedence: 10,
         },
         OperatorInfo {
             op_type: "Assignment".into(),
             operator: "*=".into(),
             name: "MultiplyAssign".into(),
+            description: "Multiplies a variable by a value.".into(),
             precedence: 10,
         },
         OperatorInfo {
             op_type: "Assignment".into(),
             operator: "/=".into(),
             name: "DivideAssign".into(),
+            description: "Divides a variable by a value.".into(),
             precedence: 10,
         },
         OperatorInfo {
             op_type: "Comparison".into(),
             operator: "==".into(),
             name: "Equal".into(),
+            description: "Checks if two values are equal.".into(),
             precedence: 80,
         },
         OperatorInfo {
             op_type: "Comparison".into(),
             operator: "!=".into(),
             name: "NotEqual".into(),
+            description: "Checks if two values are not equal.".into(),
             precedence: 80,
         },
         OperatorInfo {
             op_type: "Comparison".into(),
             operator: "<".into(),
             name: "LessThan".into(),
+            description: "Checks if a value is less than another.".into(),
             precedence: 80,
         },
         OperatorInfo {
             op_type: "Comparison".into(),
             operator: "<=".into(),
             name: "LessThanOrEqual".into(),
+            description: "Checks if a value is less than or equal to another.".into(),
             precedence: 80,
         },
         OperatorInfo {
             op_type: "Comparison".into(),
             operator: ">".into(),
             name: "GreaterThan".into(),
+            description: "Checks if a value is greater than another.".into(),
             precedence: 80,
         },
         OperatorInfo {
             op_type: "Comparison".into(),
             operator: ">=".into(),
             name: "GreaterThanOrEqual".into(),
+            description: "Checks if a value is greater than or equal to another.".into(),
             precedence: 80,
         },
         OperatorInfo {
             op_type: "Comparison".into(),
             operator: "=~".into(),
             name: "RegexMatch".into(),
+            description: "Checks if a value matches a regular expression.".into(),
             precedence: 80,
         },
         OperatorInfo {
             op_type: "Comparison".into(),
             operator: "!~".into(),
             name: "NotRegexMatch".into(),
+            description: "Checks if a value does not match a regular expression.".into(),
             precedence: 80,
         },
         OperatorInfo {
             op_type: "Comparison".into(),
             operator: "in".into(),
             name: "In".into(),
+            description: "Checks if a value is in a list or string.".into(),
             precedence: 80,
         },
         OperatorInfo {
             op_type: "Comparison".into(),
             operator: "not-in".into(),
             name: "NotIn".into(),
+            description: "Checks if a value is not in a list or string.".into(),
             precedence: 80,
         },
         OperatorInfo {
             op_type: "Comparison".into(),
             operator: "starts-with".into(),
             name: "StartsWith".into(),
+            description: "Checks if a string starts with another.".into(),
             precedence: 80,
         },
         OperatorInfo {
             op_type: "Comparison".into(),
             operator: "ends-with".into(),
             name: "EndsWith".into(),
+            description: "Checks if a string ends with another.".into(),
             precedence: 80,
         },
+        OperatorInfo {
+            op_type: "Comparison".into(),
+            operator: "not".into(),
+            name: "UnaryNot".into(),
+            description: "Negates a value or expression.".into(),
+            precedence: 0,
+        },
         OperatorInfo {
             op_type: "Math".into(),
             operator: "+".into(),
             name: "Plus".into(),
+            description: "Adds two values.".into(),
             precedence: 90,
         },
         OperatorInfo {
             op_type: "Math".into(),
             operator: "++".into(),
             name: "Append".into(),
+            description: "Appends two lists or a list and a value.".into(),
             precedence: 80,
         },
         OperatorInfo {
             op_type: "Math".into(),
             operator: "-".into(),
             name: "Minus".into(),
+            description: "Subtracts two values.".into(),
             precedence: 90,
         },
         OperatorInfo {
             op_type: "Math".into(),
             operator: "*".into(),
             name: "Multiply".into(),
+            description: "Multiplies two values.".into(),
             precedence: 95,
         },
         OperatorInfo {
             op_type: "Math".into(),
             operator: "/".into(),
             name: "Divide".into(),
+            description: "Divides two values.".into(),
             precedence: 95,
         },
         OperatorInfo {
             op_type: "Math".into(),
             operator: "//".into(),
             name: "FloorDivision".into(),
+            description: "Divides two values and floors the result.".into(),
             precedence: 95,
         },
         OperatorInfo {
             op_type: "Math".into(),
             operator: "mod".into(),
             name: "Modulo".into(),
+            description: "Divides two values and returns the remainder.".into(),
             precedence: 95,
         },
         OperatorInfo {
             op_type: "Math".into(),
             operator: "**".into(),
             name: "Pow ".into(),
+            description: "Raises one value to the power of another.".into(),
             precedence: 100,
         },
         OperatorInfo {
             op_type: "Bitwise".into(),
             operator: "bit-or".into(),
             name: "BitOr".into(),
+            description: "Performs a bitwise OR on two values.".into(),
             precedence: 60,
         },
         OperatorInfo {
             op_type: "Bitwise".into(),
             operator: "bit-xor".into(),
             name: "BitXor".into(),
+            description: "Performs a bitwise XOR on two values.".into(),
             precedence: 70,
         },
         OperatorInfo {
             op_type: "Bitwise".into(),
             operator: "bit-and".into(),
             name: "BitAnd".into(),
+            description: "Performs a bitwise AND on two values.".into(),
             precedence: 75,
         },
         OperatorInfo {
             op_type: "Bitwise".into(),
             operator: "bit-shl".into(),
             name: "ShiftLeft".into(),
+            description: "Shifts a value left by another.".into(),
             precedence: 85,
         },
         OperatorInfo {
             op_type: "Bitwise".into(),
             operator: "bit-shr".into(),
             name: "ShiftRight".into(),
+            description: "Shifts a value right by another.".into(),
             precedence: 85,
         },
         OperatorInfo {
             op_type: "Boolean".into(),
             operator: "&&".into(),
             name: "And".into(),
+            description: "Deprecated. Checks if two values are true.".into(),
             precedence: 50,
         },
         OperatorInfo {
             op_type: "Boolean".into(),
             operator: "and".into(),
             name: "And".into(),
+            description: "Checks if two values are true.".into(),
             precedence: 50,
         },
         OperatorInfo {
             op_type: "Boolean".into(),
             operator: "||".into(),
             name: "Or".into(),
+            description: "Deprecated. Checks if either value is true.".into(),
             precedence: 40,
         },
         OperatorInfo {
             op_type: "Boolean".into(),
             operator: "or".into(),
             name: "Or".into(),
+            description: "Checks if either value is true.".into(),
             precedence: 40,
         },
         OperatorInfo {
             op_type: "Boolean".into(),
             operator: "xor".into(),
             name: "Xor".into(),
+            description: "Checks if one value is true and the other is false.".into(),
             precedence: 45,
         },
     ]