This is exactly the reason to make the documentation efforts the top priority and to start it now. We need to make sure that the documentation improves as the project grows, right now there's an impression that the documentation coverage and quality don't keep up with all the changes. If we dismiss this as a priority, the state of things will only become worse in the next five to ten years. If the declared goal is to make Swift available for everyone on all platforms, the community should be able to participate in that instead of being excluded.
By "being excluded" I mean only the impression that people get when they are introduced to the project, just as @Zollerboy1 highlighted above. One obviously could answer "everything is open source, what else do you need? We should be happy with what we've got, it could have been closed source", but that won't help us attract more people to the community, maybe even the opposite. There's still the impression that Swift is "an Apple language" and I find it hard convincing people otherwise for exactly these reasons. A lot of it is more similar to "source code dumps" that Apple have been doing before they started using GitHub. I appreciate they started accepting pull requests, but this is only the first step and it's clearly not enough.