Install script

[mfinifter]

We need a script that 'installs' zfs-auto-backup, which means it just sets up the cron jobs correctly. Bonus if we make an actual ubuntu package.

[joelweinberger]

This isn't entirely what we want, but I created a Makefile with install and uninstall directives as of 0d4d643 that temporarily improves the status quo. Obviously, we still want a package and we need something to setup cron jobs appropriately.