Add NixOS flake

flake.nix

@@ -0,0 +1,26 @@
+{
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/master";
+  inputs.systems.url = "github:nix-systems/default";
+
+  outputs = {
+    self,
+    nixpkgs,
+    flake-utils,
+    systems,
+  }:
+    flake-utils.lib.eachSystem (import systems)
+    (system: let
+      pkgs = import nixpkgs {
+        inherit system;
+      };
+    in {
+      devShells.default = pkgs.mkShell {
+        buildInputs = [
+          pkgs.nodejs
+
+          # Package manager
+          pkgs.nodePackages.pnpm
+        ];
+      };
+    });
+}