Yarn workspace with transformer plugin (/gatsby-transformer-markdoc) and example site (/site).
Clone, run yarn && yarn workspace site develop to (hopefully) develop locally.
These could use a rename but the /site/markdocs directory is where the example .md and .mdoc files live that we source via gatsby-source-filesystem (see gatsby-config.js), while /markdoc is attempting to mimic what rough standard for framework configuration that was set in the Next.js plugin.