Add documentation .md files to test the pages job

Problem/Motivation

We do not have any downstream test coverage for .md files and for the pages job.

Proposed resolution

From #20 in #3503337-20: Plan for initial codebase →

Maybe we can use the "main" branch to generate a small documentation site, where we have a page for each branch explaining what each branch is about. Something short but that will be enough to check md files and the pages job.

Remaining tasks