I have written and curated some content to explain how to use a docinfo file. If you're interested, I'd love to have some people review the section to make sure I'm not introducing any errors or missing vital information. The pending pull request and supporting discussion is here.
As noted in the pull request, I've already identified a few changes I will make, including:
1. The bulk of the docinfo content should probably be moved to the producing or rendering part of the user manual, with just a brief description and a link included in the section's current location.
2. Create transitions between the sections, currently they end rather bluntly.
3. Create content about what a footer can contain in general - not just in the sense of a docinfo file.
4. Remove the table captions from the entire user manual.