docs(guide): clarify example

docs/content/guide/dev_guide.services.injecting_controllers.ngdoc

@@ -57,6 +57,7 @@ myController.$inject = ['$scope','notify'];
   <p>Let's try this simple notify service, injected into the controller...</p>
   <input ng-init="message='test'" ng-model="message" >
   <button ng-click="callNotify(message);">NOTIFY</button>
+  <p>(you have to click 3 times to see an alert)</p>
 </div>
 </doc:source>
 <doc:scenario>