Added instructions to change time zone in GitLab CE

doc/workflow/timezone.md

+# Changing your time zone
+
+GitLab defaults its time zone to UTC. It has a global timezone configuration parameter in config/application.rb. 
+
+To update, add the time zone that best applies to your location. Here are two examples:
+```
+gitlab_rails['time_zone'] = 'America/New_York' 
+```
+or
+```
+gitlab_rails['time_zone'] = 'Europe/Brussels'
+```
+
+After you added this field, reconfigure and restart:
+```
+gitlab-ctl reconfigure
+gitlab-ctl restart
+```
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