Use origin to compare so it is not dependent on checking out the branch before.

doc/update/7.2-to-7.3.md

@@ -92,7 +92,7 @@ sudo cp lib/support/init.d/gitlab /etc/init.d/gitlab
 There are new configuration options available for gitlab.yml. View them with the command below and apply them to your current gitlab.yml.
 ```
-git diff 7-2-stable:config/gitlab.yml.example 7-3-stable:config/gitlab.yml.example
+git diff origin/7-2-stable:config/gitlab.yml.example origin/7-3-stable:config/gitlab.yml.example
 ```
 ```