We could add a page to the official documentation linking to third-party documentation and tutorials. You’d just have to upload the PDF somewhere publicly accessible.
I guess maintaining the guide as a forum post as suggested by ByteHamster could work, too.
Right now our documentation is quite outdated. It is integrated into the website and the navigation is a bit confusing. We plan to extract the documentation to a separate site. This is currently work in progress.
We have created a new repository for the documentation and Art is currently working on the infrastructure: GitHub - k9mail/k9mail-docs: [WIP] K-9 Mail documentation
Help with the official documentation would be very much appreciated. I’ve created a couple of issues with initial work that needs to be done.