Add more info 404.html

doc.zih.tu-dresden.de/tud_theme/404.html

 {% extends "main.html" %}
+
 {% block content %}
-  <h1>This page has been moved, please use the search functionality.</h1>
-  If you have Javascript disabled, please enable it to see the search bar.
+
+<h3 style="text-align:center">The page you requested could not be found.</h3>
+<h3 style="text-align:center">Probably it has been moved, please use the search bar.</h3>
+
+<p style="text-align:center">If you have Javascript disabled, please enable it to see the search bar. </p>
+
 {% endblock %}