Merge pull request #23 from quadland/UpdateEventsDocumentation

Update events documentation

README.md

@@ -78,12 +78,16 @@ $response = $client->get('/users');
 ## Events
 Handling events.  Events are dispatched before and after the request to the remote host.
 ### Listening To Events
-``` xml
-        <service id="listenerID" class="Your\ListenerClass\That\Implements\GuzzleEventListenerInterface">
-            <tag name="kernel.event_listener" event="guzzle_bundle.pre_transaction" method="onPreTransaction" service="servicename"/>
-        </service>
+```xml
+    <service id="listenerID" class="Your\ListenerClass\That\Implements\GuzzleEventListenerInterface">  
+        <tag name="kernel.event_listener" event="guzzle_bundle.pre_transaction" method="onPreTransaction" service="servicename"/>  
+    </service>  
 ```
 
+Your event Listener, or Subscriber **MUST** implement GuzzleBundle\Events\GuzzleEventListenerInterface.  
+Events dispatched are guzzle_bundle.pre_transaction, guzzle_bundle.post_transaction.  
+The service on the tag, is so that if you have multiple REST endpoints you can define which service a particular listener is interested in.
+
 ## Features
 ### Symfony Debug Toolbar / Profiler
 <img src="/Resources/doc/img/debug_logs.png" alt="Debug Logs" title="Symfony Debug Toolbar - Guzzle Logs" style="width: 360px" />