Document 'make all:<name>' (#8439)

* Document 'make all:<name>'

* add cli docs

* Apply suggestions from code review

Co-Authored-By: skullydazed <[email protected]>

Co-authored-by: skullydazed <[email protected]>

docs/cli_commands.md

@@ -57,6 +57,12 @@ Must be in keyboard directory with a default keymap, or in keymap directory for
 qmk compile
 ```
 
+**Usage for building all keyboards that support a specific keymap**:
+
+```
+qmk compile -kb all -km <keymap_name>
+```
+
 **Example**:
 ```
 $ qmk config compile.keymap=default