I tried using README files in the repo but there’s far too much friction to get most folks to bother. Google Docs tend to disappear content due to a lack of structure.
Lots of people like to generate a flurry of tiny commits but it's not necessarily the most productive way to work, even without much overhead per change. You can always bundle tiny changes together until it's worth it for you and other people like the reviewer to do the parts that don't scale downwards.
I have confluence links in my Readme, which seems to be a pretty good balance, since it's physically impossible for people to use a search bar in a wiki.