Document the WPT core team

[foolip]

@web-platform-tests/wpt-core-team there's nothing we can link to showing what the WPT core team's responsibilities are and who's in it. https://github.com/web-platform-tests/rfcs links to https://github.com/orgs/web-platform-tests/teams/wpt-core-team/ and in web-platform-tests/interop#342 I could only suggest the same.

[zcorpan]

https://web-platform-tests.org/admin/index.html#third-party-account-owners has some names for "GitHub: web-platform-tests" but it matches neither https://github.com/orgs/web-platform-tests/teams/admins nor https://github.com/orgs/web-platform-tests/teams/wpt-core-team/

[foolip]

It also doesn't match https://github.com/orgs/web-platform-tests/people?query=role%3Aowner

[gsnedders]

See also https://lists.w3.org/Archives/Public/public-test-infra/2018OctDec/0008.html and #11473