Contribution guide conflicts with pull request creation policy

[z0rimo]

The current CONTRIBUTING.md says:

Thanks for your interest in contributing! We accept pull requests.

However, when attempting to open a pull request from a fork, GitHub reports:

An owner of this repository has limited the ability to open a pull request to users that are collaborators on this repository.

I encountered this while preparing a small update for #137.

Could you clarify which behavior is intended?

• If external pull requests are intended to be accepted, the repository's pull request creation policy may need to be updated.
• If pull requests are intentionally limited to collaborators, CONTRIBUTING.md could be updated to reflect that restriction.

Either way, aligning the documented contribution process with the repository settings would help avoid confusion for contributors preparing changes from forks.