add missing {{countdown}} to countdown timer example docs

Author: bikezilla

index.html

@@ -139,7 +139,7 @@ <h3>
 
     <div class="bs-docs-example">
         <p>
-            The countdown timer <code ng-non-bindable="">&lt;timer interval=&quot;1000&quot; countdown=&quot;100&quot;/&gt;</code>
+            The countdown timer <code ng-non-bindable="">&lt;timer interval=&quot;1000&quot; countdown=&quot;100&quot;&gt;{{countdown}}&lt;/timer&gt;</code>
             will start its countdown from 100 until it reaches 0 by ticking every second</p>
 
         <h3>