Added information on base html about osbolete documentation

This is how the page will look like.

themes/hugo-geekdoc/layouts/_default/baseof.html

@@ -25,6 +25,13 @@
                 {{ partial "menu" . }}
             </aside>
             {{ end }}
+            
+            <blockquote class="container gdoc-hint danger obsolete">
+                <p><strong>WARNING</strong></p>
+                <p>
+                    This documentation is obsolete and not maintained anymore, please use new <a class="gdoc-markdown__link" href="https://docs.e-infra.cz/compute/openstack/">e-INFRA CZ documentation</a>
+                </p>  
+            </blockquote>
 
             <div class="gdoc-page">
                 {{ template "main" . }}