There's a lot of different ways to manage and track RFCs, and honestly, it's really just up to your preference, you could use github issues, discussions, pull requests, a separate repository, or an external tool. Democratized projects, like Rust, or Wayland seem to gravitate to using pull requests. Personally, I think markdown files might be a better solution than github discussions, but it's really up to however you decide it should be managed.