Wrap nixpkgs with a warning

[warn-nixpkgs] / README.md

# warn-nixpkgs

Wrap nixpkgs, but emit a warning if this one is ever accessed.

The Nix world is gradually adopting flakes and moving toward a world
where there are no longer `nix-update`-maintained channels.  During that
transition, it's nice to have system channels that still work, but emit
a warning when they are accessed to alert the user of of a gap in their
move-to-flakes.

This repo can be used as a drop-in replacement for the `nixpkgs` channel.
This repo doesn't contain `nixpkgs` -- this is merely a thin wrapper.
Configure the actual `nixpkgs` to forward to as a `nixpkgs-warned`
channel.