Document how to change the persistence password
Originally created by Tails on #5621 (Redmine)
From the current Persistent Volume Assistant and documentation there is no way of changing the password of a persistent volume.
This can be done using the GNOME Disk Utility and should be documented.
It should also be documented that, due to wear leveling on solid state media, parts of old LUKS header may be recoverable.
Feature Branch: doc/change_persistence_passphrase