Coincidentally you caught me the day I popped back (to see if there was any news on the upcoming qt5-webengine migration).
From the look of that project, it's essentially just the tarballs provided on
https://archlinuxarm.org/ converted into an ISO image. Actually I'm not sure what the point is.
But it should be quite simple to use the official archlinuxarm releases, follow the instructions to format your SD card and copy over the contents of the tarball. Then boot into the rpi and pacman -Syu calibre.