Apply suggestions from code review

Co-authored-by: Alejandro Santiago <dev@alestiago.com>

lib/game/view/game_hud.dart

@@ -2,7 +2,12 @@ import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:pinball/game/game.dart';
 
+/// {@template game_hud}
+/// Overlay of a [PinballGame] that displays the current [GameState.score] and 
+/// [GameState.balls].
+/// {@endtemplate}
 class GameHud extends StatelessWidget {
+  /// {@macro game_hud}
   const GameHud({Key? key}) : super(key: key);
 
   @override