Merge branch 'labels-mr' into 'master'

Added note about labels in MR

because of tweet https://twitter.com/apoirier1/status/624197308759035905

See merge request !1911

doc/workflow/labels.md

 # Labels
 
-In GitLab, you can easily tag issues and merge requests. If you have permission level `Developer` or higher, you can manage labels. To create, edit or delete a label, go to a project and then to `Issues` and then `Labels`.
+In GitLab, you can easily tag issues and Merge Requests. If you have permission level `Developer` or higher, you can manage labels. To create, edit or delete a label, go to a project and then to `Issues` and then `Labels`.
 
 Here you can create a new label.
 
@@ -14,3 +14,5 @@ If you want to change an existing label, press edit next to the listed label.
 You will be presented with the same form as when creating a new label.
 
 ![edit label](labels/label3.png)
+
+You can add labels to Merge Requests when you create or edit them.