Auto-generate markdown command docs (#4451)

* Finish updating

* a couple improvements

* Update renames

* cleanup examples

docs/commands/roll_down.md

@@ -0,0 +1,23 @@
+---
+title: roll down
+layout: command
+version: 0.59.0
+---
+
+Roll table rows down
+
+## Signature
+
+```> roll down --by```
+
+## Parameters
+
+ -  `--by {int}`: Number of rows to roll
+
+## Examples
+
+Rolls rows down
+```shell
+> [[a b]; [1 2] [3 4] [5 6]] | roll down
+```
+