docs: add "page source" link to sphinx documentation

Add a link to the top of the sidebar in every docs page that takes the
user back to the source code in gitlab.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20201102130926.161183-5-berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
diff --git a/docs/conf.py b/docs/conf.py
index e584f68..d40d8ff 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -177,6 +177,7 @@
 html_sidebars = {
     '**': [
         'about.html',
+        'editpage.html',
         'navigation.html',
         'searchbox.html',
     ]