set dovecot postmaster_address setting, fixes #31
refine the goals in the README
enable ufw firewall again

I had previously awkwardly disabled it because on my VPS the necessary kernel
module wasn't available. I meant to make it an option, but instead I took
out the apt-get install. Now it works for me so I'm putting everything back.
messed up markdown in the README, in 263fdb15f9328a5f4c8d9cb53eee0509ea7e05fa
Bootstrap installation in a Vagrant image
Enable quick Vagrant provisioning