Adding dev documentation for chrome.location

chrome/common/extensions/docs/templates/intros/location.html

+<p id="classSummary">
+  To create a location watch, call $ref:location.watchLocation passing in
+  the location watch details via the <code>requestInfo</code> parameter:
+</p>
+
+<pre>chrome.location.watchLocation(name, requestInfo);</pre>
+<p>
+  You'll also need to add a listener
+  to its <code>onChanged</code> event.
+  Chrome will fire this event after you create your location watch. After this,
+  it will keep firing the event every time the geographical location of your
+  computer changes until you call $ref:location.clearWatch.
+</p>
+<p>
+  Here's sample code
+  to listen for location updates:
+</p>
+<pre>
+  chrome.location.onLocationUpdate.addListener(function(position) {
+    console.log(JSON.stringify(position));
+  });
+</pre>