clarify to-do about unimplemented ability to scroll up to events

that have not yet been fetched in the timeline

src/home/room_screen.rs

@@ -1137,6 +1137,8 @@ impl Widget for RoomScreen {
                                 };
 
                                 self.redraw(cx);
+                            } else {
+                                log!("TODO: the replied-to message was not yet available in the timeline.");
                             }
                         }
                     }