Update PKGBUILD to include the GitHub URL for this fork

I noticed that the Arch Linux PKGBUILD for this thing is rather outdated, so I updated the URL to https://github.com/DaveDavenport/simpleswitcher (and added you as a contributor; I have no idea what your email is so you could edit that in later I suppose).

I guess you don't really want this if you have the intention of submitting these changes back to seanpringle/simpleswitcher, but I don't see any pull requests pertaining to the i3 stuff over there.

BTW, as an i3 user I find this thing really helpful, thanks!