Document custom command action

packages/cursorless-org-docs/src/docs/user/customization.md

@@ -204,3 +204,36 @@ _You can disable the default Cursorless reformat command by prefixing the spoken
 <user.formatters> form <user.cursorless_target>:
     user.cursorless_reformat(cursorless_target, formatters)
 ```
+
+### Experimental custom command action
+
+_NOTE that this feature is experimental. Not as thoroughly tested as the rest of Cursorless and might change in the future_
+
+`user.cursorless_custom_command(command: string, *args)`
+
+Run a custom Cursorless command by parsing the specified command string. Supports a subset of the Cursorless grammar, with **default** spoken forms (not your custom spoken forms). See https://www.cursorless.org/custom-command-railroad to see the subset of our grammar that we support today.
+
+- Utilizes default Cursorless spoken forms in the command string.
+- Optional target arguments can be interpolated in the command string. (see examples below)
+
+#### Examples
+
+In order to map `"scratch"` to perform `"chuck block"`:
+
+```talon
+scratch: user.cursorless_custom_command("chuck block")
+```
+
+To map `"scratch air"` => `"chuck block air"`
+
+```talon
+scratch <user.cursorless_target>:
+    user.cursorless_custom_command("chuck block <target>", cursorless_target)
+```
+
+To map `"combine air plus bat"` => `"bring block air after bat"`
+
+```talon
+combine <user.cursorless_target> plus <user.cursorless_target>:
+    user.cursorless_custom_command("bring block <target1> after <target2>", cursorless_target_1, cursorless_target_2)
+```