Merge branch 'link-multiple-issues' into 'master'

Added link to issue closing pattern documentation in milestones doc

Added link from Milestones doc to Issue closing pattern because I think they can be useful. Because of Tweet https://twitter.com/steenwijkict/status/619210265008205824

cc/ @sytse 

See merge request !1895

doc/api/milestones.md

@@ -87,3 +87,5 @@ Parameters:
 
 - `id` (required) - The ID of a project
 - `milestone_id` (required) - The ID of a project milestone
+
+You can close multiple issues with one Merge Request by following the [issue closing pattern documentation](http://doc.gitlab.com/ce/customization/issue_closing.html).