Clarify instructions on performing a restore on a source installation

doc/raketasks/backup_restore.md

@@ -840,11 +840,22 @@ Read more about [configuring NFS mounts](../administration/nfs.md)
 
 ### Restore for installation from source
 
+First, ensure your backup tar file is in the backup directory described in the
+`gitlab.yml` configuration:
+
+```yaml
+## Backup settings
+backup:
+  path: "tmp/backups"   # Relative paths are relative to Rails.root (default: tmp/backups/)
+```
+
+The default is `/home/git/gitlab/tmp/backups`, and it needs to be owned by the `git` user. Now, you can begin the backup procedure:
+
 ```shell
 # Stop processes that are connected to the database
 sudo service gitlab stop
 
-bundle exec rake gitlab:backup:restore RAILS_ENV=production
+sudo -u git -H bundle exec rake gitlab:backup:restore RAILS_ENV=production
 ```
 
 Example output: