I had this same question and the official answer is to post your Docs suggestion here, in this forum. About the Contributing to Ghost category - #4 by RyanF
Here’s an example of what I did, although I haven’t heard back from the Ghost team yet…I think this is a down-side of their decision not to open-source the Docs, because rather than Pull Requests, you get this confusion and threads stay open for weeks without comments: Docs Suggestion: Clarify pre-requisites in "Install from Source"
Suggestion: Allow logging in as a seeded User locally - #4 by vanm
Judging by the questions in here, I think a lot of people care about good documentation, but it seems to be slipping through the cracks.