Note async versions of event handling within EventsProvider

Author: wpaulino

lightning/src/util/events.rs

@@ -1400,6 +1400,8 @@ pub trait OnionMessageProvider {
 ///
 /// Events are processed by passing an [`EventHandler`] to [`process_pending_events`].
 ///
+/// Implementations of this trait may also feature an async version of event handling.
+///
 /// # Requirements
 ///
 /// When using this trait, [`process_pending_events`] will call [`handle_event`] for each pending