doc/nixpkgs-committers: Link instead

[roberth]

Document the policy the Nixpkgs Core team has adopted, by link.

This is technically a change in policy, hence the request for @NixOS/steering reviews

• See also README: link to updated procedures nixpkgs-committers#122

[K900]

This file is generally managed by the nixpkgs core team, not SC.

[roberth]

Not sure what you mean @K900. The Nixpkgs Core team has only adjusted the "team" part of this page.
This PR reinforces the idea that the core team manages the commit bit policy, but by referring to "this file" you are either supporting the PR, or presenting factually incorrect information. I suppose you meant to support the PR, but you gave a comment, not an approval. I'm confused.

[K900]

What I'm saying is that SC should not be making any changes here without explicit core team approval, and generally should not be initiating meaningful changes ever.

[mweinelt]

You requested the SC for review even though it does not own this file, that's what seemed weird to me. The SC approvals are meaningless.

[roberth]

I'm doing this entirely to help the core team. Let me fix the request for review