index: sort projects within postmarketos

Sort by relevance to developers, so pmaports would go on the very top once we add it, and bpo stays at the bottom. I've considered sorting alphabetically as well, but that would put bpo on top which is only relevant to few people. I think the docs are in good enough shape to remove from WIP now, at least it uses the new theme and maybe we want to improve the BPO docs in the future too (even if we are considering replacing BPO).