Auto-generate markdown command docs (#4451)

* Finish updating

* a couple improvements

* Update renames

* cleanup examples

docs/commands/dfr_str-slice.md

@@ -0,0 +1,24 @@
+---
+title: dfr str-slice
+layout: command
+version: 0.59.0
+---
+
+Slices the string from the start position until the selected length
+
+## Signature
+
+```> dfr str-slice (start) --length```
+
+## Parameters
+
+ -  `start`: start of slice
+ -  `--length {int}`: optional length
+
+## Examples
+
+Creates slices from the strings
+```shell
+> [abcded abc321 abc123] | dfr to-df | dfr str-slice 1 -l 2
+```
+