Put a link back to the index in every page footer

Signed-off-by: Shawn O. Pearce <sop@google.com>
diff --git a/Documentation/cmd-index.txt b/Documentation/cmd-index.txt
index 02fa80d..529241c 100644
--- a/Documentation/cmd-index.txt
+++ b/Documentation/cmd-index.txt
@@ -46,3 +46,7 @@
 
 link:cmd-replicate.html[gerrit replicate]::
 	Manually trigger replication, to recover a node.
+
+GERRIT
+------
+Part of link:index.html[Gerrit Code Review]