Documentation issue: verify backup

[aidhog]

In the documentation for the backup, I strongly suggest to add a step to verify that the backup was done (and to verify the volume names for older versions). If the volume names are incorrect (as happened to me, trying to update a very old Wikibase instance), empty tar.gz files are generated without warning, so the user might believe they have a backup when they do not.

[deepeshaburse]

Hi @aidhog, thanks for opening an issue. I will try to get someone on this soon :)