Auto-generate markdown command docs (#4451)

* Finish updating

* a couple improvements

* Update renames

* cleanup examples

docs/commands/to_md.md

@@ -0,0 +1,34 @@
+---
+title: to md
+layout: command
+version: 0.59.0
+---
+
+Convert table into simple Markdown
+
+## Signature
+
+```> to md --pretty --per-element```
+
+## Parameters
+
+ -  `--pretty`: Formats the Markdown table to vertically align items
+ -  `--per-element`: treat each row as markdown syntax element
+
+## Examples
+
+Outputs an MD string representing the contents of this table
+```shell
+> [[foo bar]; [1 2]] | to md
+```
+
+Optionally, output a formatted markdown string
+```shell
+> [[foo bar]; [1 2]] | to md --pretty
+```
+
+Treat each row as a markdown element
+```shell
+> [{"H1": "Welcome to Nushell" } [[foo bar]; [1 2]]] | to md --per-element --pretty
+```
+