autocomplete [nfc]: Add TODO about sorting results

This *looks* like a likely-looking place where we might add this
logic, but perhaps it belongs somewhere else? We'll take a closer
look later.

Author: chrisbobbe

lib/model/autocomplete.dart

@@ -267,7 +267,7 @@ class MentionAutocompleteView extends ChangeNotifier {
         }
       }
     }
-    return results;
+    return results; // TODO sort for most relevant first
   }
 }