Autogenerate missing docs (#3514)

* Autogenerate missing docs

* Update ansi.md

* Rename question mark command docs

* Delete empty?.md

docs/commands/let.md

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+# let
+Create a variable and give it a value.
+
+## Usage
+```shell
+> let <name> <equals> <expr> {flags} 
+ ```
+
+## Parameters
+* `<name>` the name of the variable
+* `<equals>` the equals sign
+* `<expr>` the value for the variable
+
+## Flags
+* -h, --help: Display this help message
+
+## Examples
+  Assign a simple value to a variable
+```shell
+> let x = 3
+ ```
+
+  Assign the result of an expression to a variable
+```shell
+> let result = (3 + 7); echo $result
+ ```
+
+  Create a variable using the full name
+```shell
+> let $three = 3
+ ```
+