Merge branch 'docs-api-email' into 'master'

Add email clarification

See merge request gitlab-org/gitlab-ce!27645

doc/api/users.md

@@ -33,7 +33,7 @@ GET /users
 ]
 ```
 
-You can also search for users by email or username with: `/users?search=John`
+You can also search for users by name or primary email using `?search=`. For example. `/users?search=John`.
 
 In addition, you can lookup users by username: