The GPL defines the term Source Code as "the preferred format for making changes". This means that if your repository just contains some documentation files in a readily editable format (text, markdown, OpenOffice, MS Word, etc.) then those files count as their own source format.
Monorepos have become very popular since google does it. I'm not a fan for most situations.
Monorepos seem to make sense for:
complex projects without any easy compartmentalization
folks that have lots of CI/CD experience and they're happy to customize tools to work with the monorepo.
It doesn't sound like you're a large organization. ...