add flake file

flake.nix

@@ -0,0 +1,37 @@
+# flake.nix
+{
+  description = "Haskell Development Environment with GTK and WebKit";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/7b6142dae006";
+  };
+
+  outputs = { self, nixpkgs }: let
+    system = "x86_64-linux";
+    pkgs = nixpkgs.legacyPackages.${system};
+  in {
+    devShells.${system}.default = pkgs.mkShell {
+      buildInputs = [
+	pkgs.haskellPackages.ghc
+	pkgs.haskellPackages.cabal-install
+	pkgs.gtk3
+	pkgs.webkitgtk
+	pkgs.pkg-config
+	pkgs.zlib
+	pkgs.glib
+	pkgs.gobject-introspection
+	pkgs.libx11
+	pkgs.gdk-pixbuf
+	pkgs.cairo
+	pkgs.pango
+	pkgs.libsoup
+	pkgs.sqlite
+      ];
+
+      shellHook = ''
+	echo "Welcome to the Haskell shell for Svitak."
+	export PKG_CONFIG_PATH=${pkgs.gobject-introspection}/lib/pkgconfig
+      '';
+    };
+  };
+}