export binary caches via flake

flake.nix

@@ -1,6 +1,15 @@
 {
   description = "NixOS configuration of our builders";
 
+  nixConfig.extra-substituters = [
+    "https://nix-community.cachix.org"
+    "https://nixpkgs-update.cachix.org"
+  ];
+  nixConfig.extra-trusted-public-keys = [
+    "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+    "nixpkgs-update.cachix.org-1:6y6Z2JdoL3APdu6/+Iy8eZX2ajf09e4EE9SnxSML1W8="
+  ];
+
   inputs = {
     #nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable-small";
     # https://github.com/NixOS/nixpkgs/pull/168186

nix/nix.conf

@@ -1,2 +0,0 @@
-substituters = https://cache.nixos.org https://nix-community.cachix.org/ https://nixpkgs-update.cachix.org/
-trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs= nixpkgs-update.cachix.org-1:6y6Z2JdoL3APdu6/+Iy8eZX2ajf09e4EE9SnxSML1W8=

shell.nix

@@ -31,6 +31,5 @@ mkShell {
 
   shellHook = ''
     export CLOUDFLARE_API_TOKEN=$(< ./secrets/cloudflare-api-token)
-    export NIX_USER_CONF_FILES="$(pwd)/nix/nix.conf";
   '';
 }