Add comments to highlight where we'll need m.widget support

For https://github.com/vector-im/riot-web/issues/13111

src/stores/ActiveWidgetStore.js

@@ -64,6 +64,7 @@ class ActiveWidgetStore extends EventEmitter {
         // Everything else relies on views listening for events and calling setters
         // on this class which is terrible. This store should just listen for events
         // and keep itself up to date.
+        // TODO: Enable support for m.widget event type (https://github.com/vector-im/riot-web/issues/13111)
         if (ev.getType() !== 'im.vector.modular.widgets') return;
 
         if (ev.getStateKey() === this._persistentWidgetId) {