flake: add nixos-generators for output pianonix-image

flake.nix

@@ -10,6 +10,11 @@
     nix-colors.url = "github:misterio77/nix-colors";
     deploy-rs.url = "github:serokell/deploy-rs";
 
+    nixos-generators = {
+      url = "github:nix-community/nixos-generators";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+
     home-manager = {
       url = "github:nix-community/home-manager/release-25.05";
       inputs.nixpkgs.follows = "nixpkgs";
@@ -84,7 +89,7 @@
 
     packages = forEachSystem (pkgs: import ./pkgs {inherit pkgs;});
     devShells = forEachSystem (pkgs: import ./shell.nix {inherit pkgs;});
-    formatter = forEachSystem (pkgs: pkgs.alejandra);
+    formatter = forEachSystem (pkgs: pkgs.alejandra); # nix fmt *
 
     nixosConfigurations = {
       # Main laptop
@@ -183,5 +188,15 @@
         };
       };
     };
+
+    # substitutes: nixos-generate --flake .#pianonix -f sd-aarch64 --system aarch64-linux
+    pianonix-image = inputs.nixos-generators.nixosGenerate {
+      system = "aarch64-linux";
+      format = "sd-aarch64";
+      modules = [./hosts/pianonix];
+      specialArgs = {
+        inherit inputs outputs;
+      };
+    };
   };
 }