update l ink to GCZ docs

Author: martenson

templates/usegalaxy.cz/static/welcome.html

@@ -40,7 +40,7 @@
             </p>
             <p>
                 Please visit our
-                <a href="https://docs.metacentrum.cz/en/docs/related/galaxy" target="_blank"
+                <a href="https://docs.metacentrum.cz/en/docs/graphical/usegalaxy" target="_blank"
                     class="reference">Documentation</a>
                 for details about using this service. In case of any further
                 questions, please contact us at