added a bunch of nixos modules

modules/networking/mullvad.nix

@@ -0,0 +1,6 @@
+{ ... }: {
+  flake.modules.nixos.mullvad = {
+    services.mullvad-vpn.enable = true;
+    services.mullvad-vpn.gui.enable = true;
+  };
+}

modules/networking/networking.nix

@@ -0,0 +1,16 @@
+{ self, ... }:
+{
+  flake.modules.nixos.networking = { pkgs, ... }: {
+
+    imports = [
+      self.modules.nixos.mullvad
+    ];
+
+    networking.networkmanager.enable = true;
+
+    environment.variables = {
+      PKG_CONFIG_PATH = "${pkgs.openssl.dev}/lib/pkgconfig";
+    };
+
+  };
+}