Update about.html with link to backend.

Author: simi

app/templates/about.html

@@ -86,7 +86,7 @@ <h3>
         Help us improve this service
       </h3>
       <p>
-        This application uses <a href="https://github.com/dalibo/pev2" class="font-weight-bold">PEV2</a> JS library to analyze and display the plan.
+        This application uses <a href="https://github.com/dalibo/pev2" class="font-weight-bold">PEV2</a> JS library to analyze and display the plan and <a href="https://https://github.com/dalibo/explain.dalibo.com/" class=font-weight-bold">explain.dalibo.com Flask application</a> to persist plans.
       </p>
       <p>
         Please report bugs on <a href="https://github.com/dalibo/pev2/issues"><i class="fab fa-github"></i> github</a>.