Auto-generate markdown command docs (#4451)

* Finish updating

* a couple improvements

* Update renames

* cleanup examples

docs/commands/dfr_append.md

@@ -0,0 +1,31 @@
+---
+title: dfr append
+layout: command
+version: 0.59.0
+---
+
+Appends a new dataframe
+
+## Signature
+
+```> dfr append (other) --col```
+
+## Parameters
+
+ -  `other`: dataframe to be appended
+ -  `--col`: appends in col orientation
+
+## Examples
+
+Appends a dataframe as new columns
+```shell
+> let a = ([[a b]; [1 2] [3 4]] | dfr to-df);
+    $a | dfr append $a
+```
+
+Appends a dataframe merging at the end of columns
+```shell
+> let a = ([[a b]; [1 2] [3 4]] | dfr to-df);
+    $a | dfr append $a --col
+```
+