Add devShell to flake

flake.nix

@@ -18,6 +18,12 @@
           ];
       };
 
+      forAllSystems = function:
+        nixpkgs.lib.genAttrs [
+          "x86_64-linux"
+          "aarch64-darwin"
+        ] (system: function nixpkgs.legacyPackages.${system});
+      
     in
       {
         nixosConfigurations = {
@@ -30,5 +36,11 @@
             ];
           };
         };
+
+        devShells = forAllSystems (pkgs: {
+          default = pkgs.mkShell {
+            buildInputs = [ pkgs.nixos-rebuild ];
+          };
+        });
       };
 }