The source tarball is generated with arch.sh, and gets put into the archpackage subdirectory of the project.  When building with OBS just upload that, plus the PKGBUILD.  See https://build.opensuse.org/package/show/home:motters:pybitmessage/pybitmessage-0.3.4

It would be entirely possible to pull the latest code from github, but I assume that if you're distributing source code then it's not a good idea to have it dependent upon a particular hosting service.