Add Arch Linux PKGBUILD

Note that this package is loosely based on @andrewd18's currently defunct PKGBUILD in the [AUR](https://aur.archlinux.org/packages/openskyscraper-git/). I've posted this updated PKGBUILD there as well.

Andrew is still listed as the package maintainer here, but this can be changed if he no longer wishes to be should this be accepted upstream.