Adding flake for Nix users

flake.nix

@@ -0,0 +1,22 @@
+{
+  inputs = {
+    # nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    systems.url = "github:nix-systems/default";
+  };
+
+  outputs =
+    { systems, nixpkgs, ... }@inputs:
+    let
+      eachSystem = f: nixpkgs.lib.genAttrs (import systems) (system: f nixpkgs.legacyPackages.${system});
+    in
+    {
+      devShells = eachSystem (pkgs: {
+        default = pkgs.mkShell {
+          buildInputs = [
+            pkgs.gnumake
+            pkgs.zip
+          ];
+        };
+      });
+    };
+}