add nix development flake

flake.nix

@@ -0,0 +1,40 @@
+{
+  description = "A Nix-flake-based development environment for OpenStApps";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  outputs = { self, nixpkgs }:
+    let
+      overlays = [
+        (final: prev: rec {
+          nodejs = prev.nodejs-18_x;
+          chrome = prev.google-chrome;
+          firefox = prev.firefox;
+          webkit = prev.epiphany; # Safari-ish browser
+        })
+      ];
+      supportedSystems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
+      forEachSupportedSystem = f: nixpkgs.lib.genAttrs supportedSystems (system: f {
+        pkgs = import nixpkgs {
+	  inherit overlays system;
+	  config.allowUnfree = true;
+	};
+      });
+    in
+    {
+      devShells = forEachSupportedSystem ({ pkgs }:
+      let
+        python = (pkgs.python311.withPackages(ps: with ps; [ brotli fonttools ] ++ (with fonttools.optional-dependencies; [ woff ])));
+      in
+      {
+        default = pkgs.mkShell {
+          packages = with pkgs; [
+            node2nix
+            nodejs
+            python
+            firefox
+            chrome
+            webkit
+          ];
+        };
+      });
+    };
+}