Typo Fix --> .html to .adoc

Author: vikram-redhat

admin_guide/index.adoc

@@ -95,7 +95,7 @@ resource type.
 |View (get/list/watch) certain resources like
 xref:../dev_guide/events.adoc#dev-guide-events[events],
 xref:../admin_guide/manage_rbac.adoc#managing-role-bindings[nodes],
-xref:../architecture/additional_concepts/storage.html#persistent-volumes[persistent
+xref:../architecture/additional_concepts/storage.adoc#persistent-volumes[persistent
 volumes], and
 xref:../admin_guide/manage_scc.adoc#admin-guide-manage-scc[security context
 constraints].