generate (encrypted) backup with script for reimport

[steveej]

thanks for the helpful script! 🙂

as per the title of this issue, it would be neat to have a convenient way to get the data back into another andOTP instance.

[steveej]

by chance i tried to store the JSON output to a file and restore this file as an unencrypted backup, and it worked!

so all that's left to solve this issue is add documentation wherever people most likely see that 👍