Merge branch 'add-image-to-backup-task' into 'master'

Add image to backup task

doc/raketasks/backup_restore.md

 # Backup restore
+![backup banner](backup_hrz.png)
+
 ## Create a backup of the GitLab system
 Creates a backup archive of the database and all repositories. This archive will be saved in backup_path (see `config/gitlab.yml`).