[mob][photos] Add comment

mobile/lib/ui/viewer/search/result/magic_result_screen.dart

@@ -15,6 +15,8 @@ import 'package:photos/ui/viewer/gallery/gallery_app_bar_widget.dart';
 import "package:photos/ui/viewer/gallery/state/selection_state.dart";
 
 class MagicResultScreen extends StatefulWidget {
+  ///This widget expects [files] to be sorted by most relelvant first to the
+  ///magic search query.
   final List<EnteFile> files;
   final String name;
   final String heroTag;