Would an ISO of Raspbian Lite be too large for Github? The zip file clock in around 350MB. If Github doesn't care, an image for Pi 3B+ and Pi zero could be hosted there (with an additional set for the baseboards as well...4 total).
Otherwise,
@theatrus has a pre-built config.txt on his git repo for his base board. Maybe something like that for a generic reef-pi build, along with a more detailed/explicit how-to. Soup to nuts - getting a headless install w/ ssh and wifi (my post above), config.txt stuff, etc. Basically consolidate all the docs from Pi and Reef-Pi into one place for new users.