Update DO Spaces documentation about GitLab backups

doc/raketasks/backup_restore.md

@@ -193,6 +193,8 @@ This example can be used for a bucket in Amsterdam (AMS3).
     gitlab_rails['backup_upload_remote_directory'] = 'my.s3.bucket'
     ```
 
+
+
 1. [Reconfigure GitLab] for the changes to take effect
 
 #### Other S3 Providers
@@ -692,3 +694,8 @@ For more information see similar questions on postgresql issue tracker[here](htt
 
 [reconfigure GitLab]: ../administration/restart_gitlab.md#omnibus-gitlab-reconfigure
 [restart GitLab]: ../administration/restart_gitlab.md#installations-from-source
+
+### 400 Bad Request on Digital Ocean Spaces
+
+If you see `400 Bad Request` by using Digital Ocean Spaces the cause may be the usage of `gitlab_rails['backup_encryption']`. You must remove or comment the line you contain `gitlab_rails['backup_encryption'] = '...'`.
+Digital Ocean Spaces doesn't implement encryption.