Add config

nixpkgs.nix

@@ -0,0 +1,8 @@
+# A nixpkgs instance that is grabbed from the pinned nixpkgs commit in the lock file
+# This is useful to avoid using channels when using legacy nix commands
+let lock = (builtins.fromJSON (builtins.readFile ./flake.lock)).nodes.nixpkgs.locked;
+in
+import (fetchTarball {
+  url = "https://github.com/nixos/nixpkgs/archive/${lock.rev}.tar.gz";
+  sha256 = lock.narHash;
+})