On GitHub, users can create a new repository named as the user. If that repository contains a README.md, GitHub renders the contents directly on the profile of the user.
This is beneficial to the social aspect and acts as another "discovery layer". The README.md is not the same as the bio on the profile as is usually used to:
- Introduce oneself
- highlight favorite/most important projects/repositories
- give context to projects/repositories
- share funny™ statistic-images/profile badges
I would also propose to keep the README.md in a repository, like on GitHub, as that ways it's possible to track changes.