Put a link to the tour in the footer

So you can:
- see it again
- see it if you don’t have an account yet

app/templates/admin_template.html

@@ -91,8 +91,11 @@
           </ul>
         </div>
         <div class="column-one-third">
-          <h2>Developers</h2>
-          <a href="{{ url_for('main.documentation') }}">API documentation</a>
+          <h2>Documentation</h2>
+          <ul>
+            <li><a href="{{ url_for('main.tour', page=1) }}">Take the tour</a></li>
+            <li><a href="{{ url_for('main.documentation') }}">API documentation</a></li>
+          </ul>
         </div>
       </div>
     </div>