- Align the “frequent” release cycle with the calendar
  - The 6-month release cycle is hard to keep track of. A monthly
    release will make it much easier to remember the release date.
- Officialise the support for a stable version maintained for as long as NixOS stable
  - This is already the case in practice, it just happens that the
    “stable” Nixpkgs version is whichever version was deemed
    stable-enough at the time of the NixOS release.
    Officialise that by cutting a new major release alongside each NixOS one.

Note that this breaks whatever semver compatibility Nix might pretend to
have, but I don't think it makes sense any way.

Trim down the proposal quite a bit, making it much closer to the previous text, just more explicit about what we support.