add flake

flake.nix

@@ -0,0 +1,29 @@
+{
+  description = "Flake utils demo";
+
+  inputs.flake-utils.url = "github:numtide/flake-utils";
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let pkgs = nixpkgs.legacyPackages.${system}; in
+      rec {
+        packages = flake-utils.lib.flattenTree {
+          hello = pkgs.callPackage ./nix { pkgs = pkgs; };
+          gitAndTools = pkgs.gitAndTools;
+        };
+        defaultPackage = packages.pad-archiver;
+        apps.pad-archiver = flake-utils.lib.mkApp { drv = packages.pad-archiver; };
+        defaultApp = apps.pad-archiver;
+        devShell = pkgs.mkShell {
+          buildInputs = with pkgs; [
+            go
+            gopls
+            gotools
+            go-tools
+            go-langserver
+            gopls
+          ];
+        };
+      }
+    );
+}