minor fix to command

doc/update/6.2-to-6.3.md

@@ -62,7 +62,8 @@ sudo -u git -H bundle exec rake cache:clear RAILS_ENV=production
 TIP: to see what changed in gitlab.yml.example in this release use next command: 
 ```
-git diff 6.2-stable:config/gitlab.yml.example 6-3-stable:config/gitlab.yml.example
+git diff 6-2-stable:config/gitlab.yml.example 6-3-stable:config/gitlab.yml.example
+git diff 6-1-stable:config/gitlab.yml.example 6-3-stable:config/gitlab.yml.example # if you upgrading from 6-1
 ```
 * Make `/home/git/gitlab/config/gitlab.yml` same as https://github.com/gitlabhq/gitlabhq/blob/6-3-stable/config/gitlab.yml.example but with your settings.