WIP: First attempt at adding a testing doc to the links in the footer.

This may result in changing the developer document section completely.

app/templates/admin_template.html

@@ -110,6 +110,7 @@
             ] %}
             <li><a href="{{ url }}" target="_blank" rel="noopener noreferrer">{{ language }} client</a></li>
             {% endfor %}
+            <li><a href="{{ url_for("main.integration_testing") }}">Integration testing</a></li>
           </ul>
         </div>
       </div>