title: How to receive NSUserDefaultsDidChangeNotification iphone
body: <p>After a lot of searching I was not able to find whether you need to pass a dictionary object to:</p>
  <pre><code>[NSUserDefaultsDidChangeNotification addObserver: forKeyPath: options: context:];
  </code></pre>
  <p>and what should be provided in options if I want to be notified for even a single change in the userDefaults. Also what is keypath?</p>