docs: Add Device Art Generator for Nexus devices to d.a.c/distribute.

        <span class="en">Google Play Badges</a></li>

       <li><a href="<?cs var:toroot ?>distribute/googleplay/promote/brand.html">

        <span class="en">Brand Assets and Guidelines</a></li>

       <li><a href="<?cs var:toroot ?>distribute/promote/device-art.html">

        <span class="en">Device Art Generator</a></li>

     </ul>

   </li>