Documentarian
Whether a developer writes real documentation, judged by the depth of their project front pages.
What it tells you about a developer
Strong documentarians explain technical work to people who were outside the room when it happened. That skill compounds on a team: better onboarding, better handoffs, and easier collaboration with non-engineers, including recruiters.
A README is the front page of a repository: what the project does, how to run it, why it exists. Depth and care in a developer's project write-ups is one of the few writing samples a public work record provides.