Move branches docs to new location and copyedit

doc/README.md

@@ -66,6 +66,7 @@ Manage files and branches from the UI (user interface):
 - Branches
   - [Create a branch](user/project/repository/web_editor.md#create-a-new-branch)
   - [Protected branches](user/project/protected_branches.md#protected-branches)
+  - [Delete merged branches](user/project/repository/branches/index.md#delete-merged-branches)
 - **(EES/EEP)** [Repository Mirroring](workflow/repository_mirroring.md)
 - **(EES/EEP)** [Push rules](push_rules/push_rules.md): Additional control over pushes to your project.
 - **(EEP)** [File Locking](user/project/file_lock.md): Lock a file to avoid merge conflicts.

doc/user/project/branches.md → doc/user/project/repository/branches/index.md

 # Branches
 
-## Delete Merged Branches
+## Delete merged branches
 
 > [Introduced][ce-6449] in GitLab 8.14.
 
-![Delete Merged Branches](img/delete_merged_branches.png)
+![Delete merged branches](img/delete_merged_branches.png)
 
-This feature allows merged branches to be deleted in bulk. Only branches that have been merged and are not protected will be deleted as part of this operation.
+This feature allows merged branches to be deleted in bulk. Only branches that
+have been merged and [are not protected][protected] will be deleted as part of
+this operation.
 
-It's particularly useful to clean up old branches that were not deleting automatically when a Merge Request was merged. 
-
----
+It's particularly useful to clean up old branches that were not deleting
+automatically when a merge request was merged.
 
 [ce-6449]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6449 "Add button to delete all merged branches"
+[protected]: ../../protected_branches.md