title: GameKitHelper: Displaying Game Center leaderboards
body: <p>I am using GameKitHelper for my Cocos2d game. At some point, I will want to display the leaderboards, so I do this:</p>
  
  <pre><code>[[GameKitHelper sharedGameKitHelper] showLeaderboard];
  </code></pre>
  
  <p>But nothing happens. What should I do?</p>