Marginalia is clojure specific so I expect it will not help other than to provide ideas.
To create an arc equivalent you probably need build an arc library which provides some code inspection/dissection capabilities and ideally also be able to attach metadata to any given function or macro. With such a library you then build a script to auto generate the docs.
As for GitHub syncing; well no, I'm guessing users would need to trigger the script and then check in the updated docs.
This is still better for a few reasons...1. developers can generate docs, locally, that are in sync with the code base they are actually using (checked out or branched). 2. Even if the online docs gets out of sync for a while you're still only a script trigger away for updating all outstanding changes.
The alternative is what you just went through; having someone remind you to do the work manually as an after-thought, which I've only seen happen once.
