Improve the demo-warning.

Author: Augustin Delaporte

_theme/_templates/layout.html

@@ -44,9 +44,9 @@
         <div id="sidebar" class="col-sm-3">
             <div id="sidebar-content">
                 <div id="demo-warning">
-                    <h4>This is a demo</h4>
-                    <p>This is a demo provided by platform.sh.<br>
-                    <a href="http://symfony.com/doc/current/{{ pagename }}">Visit on symfony.com</a>.</p>
+                    <h4>Pull request build</h4>
+                    <p>Each pull request of the Symfony Documentation is automatically deployed and hosted on <a href="https://platform.sh">Platform.sh</a>.<br>
+                    Visit the page on <a href="https://symfony.com/doc/current/{{ pagename }}">symfony.com</a>.</p>
                 </div>
 
                 {%- include "globaltoc.html" %}