Auto-generate markdown command docs (#4451)

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* cleanup examples

docs/commands/path_join.md

@@ -0,0 +1,39 @@
+---
+title: path join
+layout: command
+version: 0.59.0
+---
+
+Join a structured path or a list of path parts.
+
+## Signature
+
+```> path join (append) --columns```
+
+## Parameters
+
+ -  `append`: Path to append to the input
+ -  `--columns {table}`: Optionally operate by column path
+
+## Examples
+
+Append a filename to a path
+```shell
+> '/home/viking' | path join spam.txt
+```
+
+Append a filename to a path inside a column
+```shell
+> ls | path join spam.txt -c [ name ]
+```
+
+Join a list of parts into a path
+```shell
+> [ '/' 'home' 'viking' 'spam.txt' ] | path join
+```
+
+Join a structured path into a path
+```shell
+> [[ parent stem extension ]; [ '/home/viking' 'spam' 'txt' ]] | path join
+```
+