Add some Debian instructions

[pkern]

We should add some user instructions on how to install and configure GLOME on Debian to Markus' presentation about GLOME

[pkern]

I added some, but it feels like the PAM module can use some work to make this better. Maybe we could avoid printing an error when we are falling back to the next module. (Like the "you need to enter at least 10 characters" we are printing today.)

Also it is somewhat annoying on a VT to parse the challenge if you don't have a QR code (although that's a very orthogonal issue).