give permission "triage" to regular contributors

Dear all,

@MartinWitt has been very active in the Spoon community, with welcoming people, answering questions, fixing bugs, adding features: https://github.com/INRIA/spoon/issues?q=sort%3Aupdated-desc+involves%3AMartinWitt+

Big kudos!

Yet, @MartinWitt cannot label issues and PRs.

To solve this problem, @MartinWitt can be given the "Triage" Github role: `Can read and clone this repository. Can also manage issues and pull requests.` ([reference documentation](https://docs.github.com/en/free-pro-team@latest/github/setting-up-and-managing-organizations-and-teams/repository-permission-levels-for-an-organization))

If you agree, you can +1 or comment here, if you disagree to give "Triage" to @MartinWitt, it's time to speak :) (deadline: oct 3)