Added tab index attributes to article/overview selector.

layout/article.html

@@ -3,10 +3,12 @@
 
     <ul class="nav nav-pills arov center">
       <li class="active">
-        <a role="tab" data-toggle="tab" href="#overview">Overview</a>
+        <a role="tab" data-toggle="tab" href="#overview"
+        tab-index="16">Overview</a>
       </li>
       <li>
-        <a role="tab" data-toggle="tab" href="#article">Sample Article</a>
+        <a role="tab" data-toggle="tab" href="#article"
+        tab-index="17">Sample Article</a>
       </li>
     </ul>