title: addProximityAlert and KEY_PROXIMITY_ENTERING
body: <p>In the documentation, when discussing <code>addProximityAlert</code> , the description about Intent confuses me a bit. Specifically this part.. </p>
  
  <blockquote>
    <p>The fired Intent will have a boolean extra added with key
    KEY_PROXIMITY_ENTERING. If the value is true, the device is entering
    the proximity region; if false, it is exiting.</p>
  </blockquote>
  
  <p>This may sound like a dumb question but.. how do I get true or false when I'm entering/ or in  a certain radius of a location. </p>
  
  <p>I'm not sure how this would work exactly.</p>
  
  <p>Do I have to write my own code and check when I'm in the proximity of my location and then have it return true and false as I'm exiting?</p>
  
  <p>I can't figure it out.</p>