Clarify from which USB stick to run the rsync when doing a backup

The new documentation on https://tails.boum.org/doc/first_steps/persistence/copy/ can be confusing, especially for people used to the former method : then, you launched the command from the newly installed USB stick, now you need to launch the command from the USB stick you want to backup. I think that the phrasing “current tails” could be clearer.

I just read the rsync manual and can’t confirm that launching the command from the USB stick with an empty persistent volume would cause no harm. if it does I think there should be a clear warning.

Feature Branch: feature/17197-clarify-rsync-command

Related issues

• Blocks #16711

Original created by @goupille on 17197 (Redmine)