code-of-conduct: use the upstream language

Provide concrete information about who to contact about CoC issues. Having unambiguous people to contact is important to resolve issues in a timely manner.

This is the primary important change, having consistent and explicit
points of contact: https://github.com/kubernetes/kubernetes-template-project/commit/98749d6b8efc612fe05d1bc42b0e0bff89f30e0a