Update links for yarn explain to Docosaurus versions

[simon-aira]

What's the problem this PR addresses?

This updates the URLs for the yarn explain command to make it work after the move from Gatsby to Docusaurus.

Resolves #6249.

How did you fix it?

• Change the version-tagged link (repo.yarnpkg.com) to what @arcanis says will be published after the next release
• Change the Github link for hint about how to help updating documentation

Checklist

• I have read the Contributing Guide.

• I have set the packages that need to be released for my changes to be effective.

• I will check that all automated PR checks pass before the PR gets reviewed.