move backup document to raketasks

doc/README.md

@@ -7,4 +7,4 @@
 + [Jobs](jobs/README.md)
 + [Runners](runners/README.md)
 + [Permissions](permissions/README.md)
-+ [Backup](backup.md)
++ [Rake Tasks](README.md)

doc/raketasks/README.md

+# Rake Tasks
+
+[Backup/Restore](backup_restore.md)
\ No newline at end of file

doc/backup.md → doc/raketasks/backup_restore.md

@@ -7,7 +7,7 @@ This archive will be saved in backup_path (see `config/application.yml`).
 The filename will be `[TIMESTAMP]_gitlab_ci_backup.tar.gz`. This timestamp can be used to restore an specific backup.
 You can only restore a backup to exactly the same version of GitLab CI that you created it on, for example 7.10.1.
-*If you are interested in GitLab backup please follow to the [GitLab backup documentation](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/raketasks/backup_restore.md)*
+*If you are interested in the GitLab backup please follow to the [GitLab backup documentation](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/raketasks/backup_restore.md)*
 ```
 # use this command if you've installed GitLab CI with the Omnibus package