Add a menu item with our discord server

Author: vgvassilev

_includes/header.html

@@ -38,6 +38,7 @@
           <li class="dropdown-item"> <a class="nav-link" href="/team_meetings">Team Meetings</a></li>
           <li class="dropdown-item"> <a class="nav-link" href="/open_projects">Open Projects</a></li>
           <li class="dropdown-item"> <a class="nav-link" target="_blank" href="https://www.linkedin.com/groups/9579649/">Follow Us</a></li>
+          <li class="dropdown-item"> <a class="nav-link" target="_blank" href="https://discord.gg/Vkv3ne4zVK">CR Discord</a></li>
         </ul>
       </li>
       <li class="nav-item">