Consolidate developer docs

Currently the developer docs are scattered in readmes in the repo

this has the benefit of being close to the action, but makes it difficult if you dont know the repo to know where the authoritative (if limited) scribblings are

the conversation previously has been mostly around publishing rst dev docs, either as part of or separate to existing docs

this add quite a bit of constraint/overhead to devs updating the docs

one possibility is we move the readmes to the wiki (and i guess increase write access to that)

this would at least allow easier structuring/linking/etc but without the constraints of producing valid/well-formed rst