Add omnibus-gitlab configuration example.

doc/reply_by_email/README.md

@@ -99,7 +99,30 @@ In this example, we'll use the Gmail address `gitlab-replies@gmail.com`.
 
 ### Omnibus package installations
 
-TODO
+In `/etc/gitlab/gitlab.rb`:
+
+```ruby
+
+gitlab_rails['reply_by_email_enabled'] = true
+gitlab_rails['reply_by_email_address'] = "gitlab-replies+%{reply_key}@gmail.com"
+gitlab_rails['reply_by_email_host'] = "imap.gmail.com" # IMAP server host
+gitlab_rails['reply_by_email_port'] = 993 # IMAP server port
+gitlab_rails['reply_by_email_ssl'] = true # Whether the IMAP server uses SSL
+gitlab_rails['reply_by_email_email'] = "gitlab-replies@gmail.com"  # Email account username. Usually the full email address.
+gitlab_rails['reply_by_email_password'] = "password" # Email account password
+gitlab_rails['reply_by_email_mailbox_name'] = "inbox" # The name of the mailbox where incoming mail will end up.
+```
+
+and run `sudo gitlab-ctl reconfigure` for changes to take effect.
+
+After reconfigure run has been successfully completed you will have the following commands available:
+
+```bash
+sudo gitlab-ctl status mailroom
+sudo gitlab-ctl stop mailroom
+sudo gitlab-ctl start mailroom
+sudo gitlab-ctl restart mailroom
+```
 
 ### Development