OBS: Add support for Arch Linux

[jwrober]

Is your feature request related to a problem? Please describe.
OBS integration is new. Add support for Arch Linux.

Describe the solution you'd like
Don't know exactly what we need, but we have an existing developer who maintains that package manually. Work with him to migrate over to OBS.

[lmoureaux]

Arch is kind of an outlier. Users are used to fetching things that are not in the repo from the AUR (a repo with recipes you can run to build it yourself), and there are great tools for that. Freeciv21 is here and the PKGBUILD is here. It's a very simple system.