Update userguide/dockervolumes - fixes issue #12052

Signed-off-by: Evgeny Lukianchikov <mail@eluck.me>

docs/sources/userguide/dockervolumes.md

@@ -205,7 +205,7 @@ elsewhere. Create a new container.
 
 Then un-tar the backup file in the new container's data volume.
 
-    $ docker run --volumes-from dbdata2 -v $(pwd):/backup busybox tar xvf /backup/backup.tar
+    $ docker run --volumes-from dbdata2 -v $(pwd):/backup ubuntu cd /dbdata && tar xvf /backup/backup.tar
 
 You can use the techniques above to automate backup, migration and
 restore testing using your preferred tools.