The only way for documentation to be part of CI (IMO) is for missing documentation to cause failed builds. There are a few ways I could think of to enforce this but is there anything off the shelf that does this?
It's not particularly sophisticated - just some tests which introspect the code and then use dumb pattern matching against the documentation text to check that different concepts from the code are mentioned at least once in the docs: https://simonwillison.net/2018/Jul/28/documentation-unit-tes...