Improving communities through documentation

Not sure how true that is.
But if it is true it would also be true contributing code too.

Documentation, while good, is not free.
It comes,with a significant maintenance burden of it's own ensuring it keeps up with the code itself.
Often out of date documentation is worse than no documentation.

So while I agree a short architectural overview document and a short "project goals and non goals" document are well worthwhile (and have less maintenance requirements since the goals and architecture change more slowly than the code) I am not convinced more developer documents are the best use of effort in many cases.