Auto-generate markdown command docs (#4451)

* Finish updating

* a couple improvements

* Update renames

* cleanup examples

docs/commands/help.md

@@ -1,78 +1,44 @@
-# help
+---
+title: help
+layout: command
+version: 0.59.0
+---
 
-Use `help` for more information on a command.
-Use `help commands` to list all available commands.
-Use `help <command name>` to display help about a particular command.
+Display help information about commands.
+
+## Signature
+
+```> help ...rest --find```
+
+## Parameters
+
+ -  `...rest`: the name of command to get help on
+ -  `--find {string}`: string to find in command usage
 
 ## Examples
 
-```shell
-> help
-Welcome to Nushell.
-
-Here are some tips to help you get started.
-  * help commands - list all available commands
-  * help <command name> - display help about a particular command
-
-Nushell works on the idea of a "pipeline". Pipelines are commands connected with the '|' character.
-Each stage in the pipeline works together to load, parse, and display information to you.
-
-[Examples]
-
-List the files in the current directory, sorted by size:
-    ls | sort-by size
-
-Get information about the current system:
-    sys | get host
-
-Get the processes on your system actively using CPU:
-    ps | where cpu > 0
-
-You can also learn more at https://www.nushell.sh/book/
-```
-
+show all commands and sub-commands
 ```shell
 > help commands
-────┬──────────────┬─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
- #  │ name         │ description
-────┼──────────────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
- 0  │ alias        │ Define a shortcut for another command.
- 1  │ append       │ Append the given row to the table
- 2  │ autoview     │ View the contents of the pipeline as a table or list.
- 3  │ build-string │ Builds a string from the arguments
- 4  │ cal          │ Display a calendar.
- 5  │ calc         │ Parse a math expression into a number
-...
- 83 │ where        │ Filter table to match the condition.
- 84 │ which        │ Finds a program file.
- 85 │ with-env     │ Runs a block with an environment set. Eg) with-env [NAME 'foo'] { echo $nu.env.NAME }
- 86 │ wrap         │ Wraps the given data in a table.
-────┴──────────────┴─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
 ```
 
+generate documentation
 ```shell
-> help cd
-Change to a new path.
-
-Usage:
-  > cd (directory) {flags}
-
-Parameters:
-  (directory) the directory to change to
-
-Flags:
-  -h, --help: Display this help message
-
-Examples:
-  Change to a new directory called 'dirname'
-  > cd dirname
-
-  Change to your home directory
-  > cd
-
-  Change to your home directory (alternate version)
-  > cd ~
-
-  Change to the previous directory
-  > cd -
+> help generate_docs
 ```
+
+show help for single command
+```shell
+> help match
+```
+
+show help for single sub-command
+```shell
+> help str lpad
+```
+
+search for string in command usage
+```shell
+> help --find char
+```
+