docs: Document obs_frontend_recording_add_chapter()

docs/sphinx/reference-frontend-api.rst

@@ -647,6 +647,17 @@ Functions
 
 ---------------------------------------
 
+.. function:: bool obs_frontend_recording_add_chapter(const char *name)
+
+   Asks OBS to insert a chapter marker at the current output time into the recording.
+
+   :param name: The name for the chapter, may be *NULL* to use an automatically generated name ("Unnamed <Chapter number>" or localized equivalent).
+   :return: *true* if insertion was successful, *false* if recording is inactive, paused, or if chapter insertion is not supported by the current output.
+
+   .. versionadded:: 30.2
+
+---------------------------------------
+
 .. function:: void obs_frontend_replay_buffer_start(void)
 
    Starts the replay buffer.