Follow-up to #14

For the registered trademark to really be useful, we should collectively agree on a trademark policy for enforcing it.

Started some investigation on https://nixos-foundation.notion.site/Policy-5c5b2d0dbce141689dcc6f6fb49f3d64. Once I get enough understanding of the design space, I'll open a PR here with a draft proposal so that we can discuss it more widely.