Auto-generate markdown command docs (#4451)

* Finish updating

* a couple improvements

* Update renames

* cleanup examples

docs/commands/echo.md

@@ -1,20 +1,28 @@
-# echo
+---
+title: echo
+layout: command
+version: 0.59.0
+---
 
-Use `echo` to repeat arguments back to the user
+Echo the arguments back to the user.
+
+## Signature
+
+```> echo ...rest```
+
+## Parameters
+
+ -  `...rest`: the values to echo
 
 ## Examples
 
+Put a hello message in the pipeline
 ```shell
-> echo Hello world
-───┬───────
- # │
-───┼───────
- 0 │ Hello
- 1 │ world
-───┴───────
+> echo 'hello'
 ```
 
+Print the value of the special '$nu' variable
 ```shell
-> echo "Hello, world!"
-Hello, world!
+> echo $nu
 ```
+