Update index.html

Author: AionSystem

case-studies/index.html

@@ -495,6 +495,7 @@
     <li><a href="/stack/">Stack</a></li>
     <li><a href="/certify/">Certify</a></li>
     <li><a href="/submissions/">Submissions</a></li>
+    <li><a href="/dev-tools/">Dev-Tools</a></li>
     <li><a href="/case-studies/" class="active">Case Studies</a></li>
     <li><a href="/about/">About</a></li>
   </ul>