Add steps, how to recover from Borg backup

It should be something like this:

1. Download the last (or preferred) version from the Borg repository.
2. Convert directories to `.tar.gz` archives (extracted in add-on's backup procedure).
3. Tar the whole directory and give it a good name.
4. Recover Home Assistant via the tar archive.

Maybe a script could be prepared for simple recovery, too.