nix: switching to using flakes

nix/flake.nix

@@ -0,0 +1,29 @@
+  {
+    inputs.nixpkgs.url = "nixpkgs/nixos-22.11";
+    inputs.nixpkgs-unstable.url = "nixpkgs/nixos-unstable";
+
+    # inputs.home-manager.url = "github:nix-community/home-manager";
+
+    outputs = { self, nixpkgs, nixpkgs-unstable, ... }@attrs:
+      let
+        system = "x86_64-linux";
+        overlay-unstable = final: prev: {
+          unstable = nixpkgs-unstable.legacyPackages.${prev.system};
+          # use this variant if unfree packages are needed:
+          # unstable = import nixpkgs-unstable {
+          #   inherit system;
+          #   config.allowUnfree = true;
+          # };
+        };
+      in {
+        nixosConfigurations.nixos = nixpkgs.lib.nixosSystem {
+          inherit system;
+          specialArgs = attrs;
+          modules = [
+            # Overlays-module makes "pkgs.unstable" available in configuration.nix
+            ({ config, pkgs, ... }: { nixpkgs.overlays = [ overlay-unstable ]; })
+            ./configuration.nix
+          ];
+        };
+      };
+  }