add compatibility with encryptssh

[xhenner]

Having to type a long passphrase is not always very easy. I prefer to log into my linux system from another computer or phone, and use a password manager to copy/paste the decryption phrase. Or sometimes, I want to be able to boot my computer from afar, when I cannot plug my yubikey in it

For that, I use dropbear and encryptssh from mkinitcpio-utils

The issue is that encryptssh is lost when ykfde did successfully opened my disk. To fix it, I just touch /.done, which encryptssh use to know that the luks volume is opened.

That way, in the normal setup, when my yubikey is plugged, the boot is automatic, but if it's not, I can start my computer from afar.