As far as I can tell, the only way to find developer.puri.sm is through the blog posts. I cannot find the link anywhere else. Please add it under “Support” (link would be titled Librem 5 Developer Docs), or at least as a link in the footer. I had to try and fail several times to find the documentation before seeing the blog post, so it stands to reason this might be happening to other people too.
Also, I have not been able to figure out how to get access to the mailing list or Matrix channel. I’d like to suggest that this information should probably be prominently display in the docs, or somewhere else that’s easy to find.
Looking forward to getting involved!