Add link back to index to new config-labels documentation page

At the end of each page we are having a link back to the documentation
index. Add this link to the config-labels documentation page where this
link is missing.

Change-Id: I04686d890606924624dfee1902fcfd8c3b4289bc
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
diff --git a/Documentation/config-labels.txt b/Documentation/config-labels.txt
index 989100e..40c380c 100644
--- a/Documentation/config-labels.txt
+++ b/Documentation/config-labels.txt
@@ -247,3 +247,7 @@
 The new column will appear at the end of the table, and `-1 Do not have
 copyright` will block submit, while `+1 Copyright clear` is required to
 enable submit.
+
+GERRIT
+------
+Part of link:index.html[Gerrit Code Review]