The developer_setup.md from here is canonical from dev perspective: https://github.com/ManageIQ/guides . There is also a couple other developer setup docs there for specific cases. That is the one we update, though, admittedly, it does need Mac setup instructions, which have been a TODO item for us.
The guides are already mirrored at http://manageiq.org/documentation/development/ , though that link has still not been exposed from the base community page. I’m not sure why there is a different doc on the website for setup. I think it’s confusing. It should probably be tossed and we should point to the guides location or the mirror.