title: cocos2d: How to set a timer
body: <p>I am developing an iPhone app using cocos2d and box2d.In this app i require to set a timer.
  The timer will show the remaining time in hand of an player to reach destination...</p>
  
  <p>how can i do that.....i have drawn a scene but no sure as i am beginner how to add timer..</p>
  
  <p>thanks</p>