doc: document open pull request limit

[mcollina]

I previously set the maximum number of open pull requests for non-Collaborators to 30 to prevent excessive AI contributions and maintainer burnout. I want to reduce that limit to 10, and this change documents the new limit in the contribution guides.

[nodejs-github-bot]

Review requested:

• @nodejs/tsc

[legendecas]

Can the number be put in CONTRIBUTING.md only, so that we don't need updating 3 places if the number changes?

[avivkeller]

What's the process for users currently with more than 10 PRs, should their overflow be closed, or grandfathered in?

[Renegade334]

What's the process for users currently with more than 10 PRs, should their overflow be closed, or grandfathered in?

GH will not close them, the user is just prevented from opening more until the total drops to <10.

[evenstensberg]

lgtm

[aduh95]

What's the process for users currently with more than 10 PRs, should their overflow be closed, or grandfathered in?

GH will not close them, the user is just prevented from opening more until the total drops to <10.

IIUC GitHub would let them open more than 30, but won't let them mark as Ready for Reviews more than 30 at a time:

[aduh95]

I suggest we revert the 30-PR limit and close this PR in favor of nodejs/admin#1087. The absolute number of non-draft PRs is not saying much about the quality of a contribution, the rate the PRs are open does. The fact that GH UI indicates the limit so prominently can give users the impression that having up to 30 open PRs is OK, so IMO it's only making things worse. I'd rather have them open 50+ PRs at once so we can block them.