Any file with the '.md' extension (not just README) should render as Markdown. Bitbucket, the host I migrated from, appears to do this, e.g.: https://bitbucket.org/petrogradphilosopher/fi/src/default/pf.md
sircmpwn, it would really help me if sourcehut could render non-README files as markdown. Are there plans to implement this eventually?
This is already supported.