[Feature request] Backup/Restore function

[NinjaGobbler]

If there is a way to include backup & restore feature on this app it will be very helpful. In scenarios where if I lose the app or my phone, I will end up losing all my to-do data which is crucial for my progress. Backup & restore from the local storage is also sufficient for a great starting point and in future some cloud storage can be considered optionally if required. Please consider.

[CrateDepth]

See https://github.com/SecUSo/privacy-friendly-backup?

[0xC0FFEEC0DE]

Thanks @CrateDepth, I think this solves the issue.
With #99 a note was added to README.md about backup.
#98 suggests to add such a note to the help screen of the app too.