demo(carousel): mention 0 in interval option

Now an interval of 0 will also stop the carousel.

Author: chrisirhc

src/carousel/docs/demo.html

@@ -16,7 +16,7 @@ <h4>Slide {{$index}}</h4>
     </div>
     <div class="col-md-6">
       Interval, in milliseconds: <input type="number" class="form-control" ng-model="myInterval">
-      <br />Enter a negative number to stop the interval.
+      <br />Enter a negative number or 0 to stop the interval.
     </div>
   </div>
 </div>