Although, I have noticed that they do use README.md files in some of other other Genode Labs repositories. So maybe they do use also use markdown. Although it does just seem to be the main front page README.md file in the repository, which looks nicer on the Github web page.
https://github.com/genodelabs/genode-rpi/blob/master/README.md https://github.com/genodelabs/genode-imx/blob/master/README.md