This issue hinges on #530, but this issue can still be started async with mock/test data.

We need to add a new step to the build process that takes all user READMEs in the Hub repo, and processes them into JSON payloads for the frontend to display as Partner pages.

As mentioned in #530, each README will have a standard, enforced schema for its frontmatter. But we need to decide if we want to do anything with the main README body, or if we just want to ignore it.