I followed the "standard installation instructions", raspberry-pi-2, for setting up the sd-card, the first boot and using pacman-key. But then looked for instructions on what to do next, such as setting up a "real" user instead of "alarm", change passwords and setup sudo. For that I used the "Initial Setup on Raspberry Pi" section of these instructions.
That worked well enough, but it seems to me those additional instructions should be included in the "standard installation instructions" and should be common across all of the platforms. I'm willing to volunteer to take a stab making the necessary changes if people agree it is a good idea.