Add tip to see difference between old and new config

doc/update/6.1-to-6.2.md

@@ -51,6 +51,12 @@ sudo -u git -H bundle exec rake cache:clear RAILS_ENV=production
 
 ### 5. Update config files
 
+TIP: to see what changed in gitlab.yml.example in this release use next command: 
+
+```
+git diff 6-1-stable:config/gitlab.yml.example 6-2-stable:config/gitlab.yml.example
+```
+
 * Make `/home/git/gitlab/config/gitlab.yml` same as https://github.com/gitlabhq/gitlabhq/blob/6-2-stable/config/gitlab.yml.example but with your settings.
 * Make `/home/git/gitlab/config/unicorn.rb` same as https://github.com/gitlabhq/gitlabhq/blob/6-2-stable/config/unicorn.rb.example but with your settings.
 * Copy rack attack middleware config