docs: Document obs_group_or_scene_from_source

docs/sphinx/reference-scenes.rst

@@ -613,6 +613,13 @@ Scene Item Group Functions
 
 ---------------------
 
+.. function:: obs_scene_t *obs_group_or_scene_from_source(const obs_source_t *source)
+
+   :return: The group or scene context, or *NULL* if neither a
+            group nor a scene.  Does not increase the reference
+
+---------------------
+
 .. function:: bool obs_sceneitem_is_group(obs_sceneitem_t *item)
 
    :param item: Scene item