Merge pull request #9335 from stefan-it/documentation/timezone-clarifications

[Documentation] non-omnibus instructions for changing time zone

doc/workflow/timezone.md

 # Changing your time zone
 
-GitLab defaults its time zone to UTC. It has a global timezone configuration parameter in /etc/gitlab/gitlab.rb 
+The global time zone configuration parameter can be changed in `config/gitlab.yml`:
+```
+    # time_zone: 'UTC'
+```
+
+Uncomment and customize if you want to change the default time zone of GitLab application.
+
+To see all available time zones, run `bundle exec rake time:zones:all`.
+
+
+## Changing time zone in omnibus installations
+
+GitLab defaults its time zone to UTC. It has a global timezone configuration parameter in `/etc/gitlab/gitlab.rb`.
 
 To update, add the time zone that best applies to your location. Here are two examples:
 ```