Update documentation on issue closing pattern.

config/gitlab.yml.example

@@ -67,7 +67,7 @@ production: &base
     # This happens when the commit is pushed or merged into the default branch of a project.
     # When not specified the default issue_closing_pattern as specified below will be used.
     # Tip: you can test your closing pattern at http://rubular.com
-    # issue_closing_pattern: '((?:[Cc]los(?:e[sd]|ing)|[Ff]ix(?:e[sd]|ing)?) +(?:(?:issues? +)?#\d+(?:(?:, *| +and +)?))+)'
+    # issue_closing_pattern: '((?:[Cc]los(?:e[sd]?|ing)|[Ff]ix(?:e[sd]|ing)?) +(?:(?:issues? +)?#\d+(?:(?:, *| +and +)?))+)'
 
     ## Default project features settings
     default_projects_features:

doc/customization/issue_closing.md

 # Issue closing pattern
 
-By default you can close issues from commit messages by saying 'Closes #12' or 'Fixed #101'.
+If a commit message matches the regular expression below, all issues referenced from
+the matched text will be closed. This happens when the commit is pushed or merged
+into the default branch of a project.
 
-If you want to customize the message please do so in [gitlab.yml](https://gitlab.com/gitlab-org/gitlab-ce/blob/73b92f85bcd6c213b845cc997843a969cf0906cf/config/gitlab.yml.example#L73)
+When not specified, the default issue_closing_pattern as shown below will be used:
+
+```bash
+((?:[Cc]los(?:e[sd]?|ing)|[Ff]ix(?:e[sd]|ing)?) +(?:(?:issues? +)?#\d+(?:(?:, *| +and +)?))+)
+```
+
+For example:
+
+```
+git commit -m "Awesome commit message (Fix #20, Fixes #21 and Closes #22). This commit is also related to #17 and fixes #18, #19 and #23."
+```
+
+will close `#20`, `#21`, `#22`, `#18`, `#19` and `#23`, but `#17` won't be closed
+as it does not match the pattern. It also works with multiline commit messages.
+
+Tip: you can test this closing pattern at [http://rubular.com][1]. Use this site
+to test your own patterns.
+
+## Change the pattern
+
+For Omnibus installs you can change the default pattern in `/etc/gitlab/gitlab.rb`:
+
+```
+issue_closing_pattern: '((?:[Cc]los(?:e[sd]|ing)|[Ff]ix(?:e[sd]|ing)?) +(?:(?:issues? +)?#\d+(?:(?:, *| +and +)?))+)'
+```
+
+For manual installs you can customize the pattern in [gitlab.yml][0].
+
+[0]: https://gitlab.com/gitlab-org/gitlab-ce/blob/40c3675372320febf5264061c9bcd63db2dfd13c/config/gitlab.yml.example#L65
+[1]: http://rubular.com/r/Xmbexed1OJ