For Maintainers: managing new GSoC contributors

[samspills]

Hello @typelevel/maintainers! It is a new season of GSoC, and to try to keep things maintainable for everyone we have a new onboarding process for contributors:

1. If you get a PR or comment on an issue that (likely) is from a GSoC applicant, you can check for their GitHub handle here:
   https://typelevel.org/gsoc-onboarding/

2. If their handle is not yet there, you may direct them to make a contribution at the onboarding repo before reviewing their PR / assigning an issue to them.
   https://github.com/typelevel/gsoc-onboarding

3. If their handle is already there, you can hold them accountable to the AI policy. If you feel they are not following it, you can point it out and close the PR without review.
   https://typelevel.org/gsoc/ai.html

The onboarding repo is designed to encourage real engagement. We hope this will improve the experience for everyone 🙏

And of course, as usual you are free to apply your own judgement in handling any contributors.