Improve lost persistence.conf instructions on known issues page

instead of reconfiguring the persistent features, persistence.conf.bak can be copied to persistence.conf
- ownership of /live/persistence/TailsData_unlocked might need to be reset to root:root
- warning: live-additional-software.conf might end up lost without a backup

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information