add nix module

linux/nix/default.nix

@@ -0,0 +1,59 @@
+{ self, inputs, ... }: {
+
+  perSystem =
+    {
+      pkgs,
+      system,
+      lib,
+      ...
+    }:
+    {
+      _module.args.pkgs = import inputs.nixpkgs {
+        inherit system;
+        config = {
+          android_sdk.accept_license = true;
+          allowUnfree = true;
+        };
+      };
+
+      packages =
+        let
+          default = pkgs.callPackage ./pkg {
+            src = self;
+          };
+        in
+        {
+          inherit default;
+
+          flatpak = inputs.nix2flatpak.lib.${system}.mkFlatpak {
+            appName = "Nexus";
+            developer = "QuadRadical";
+            appId = "nexus.federated.nexus";
+            package = default;
+            runtime = "org.gnome.Platform/49";
+            permissions = {
+              share = [ "network" ];
+              sockets = [
+                "pulseaudio"
+                "fallback-x11"
+                "wayland"
+              ];
+
+              talk-names = [
+                "org.unifiedpush.Distributor.*"
+                "org.freedesktop.Notifications"
+              ];
+              devices = [ "dri" ];
+            };
+          };
+
+          gomuks = pkgs.callPackage ./pkg/gomuks.nix {
+            src = self;
+          };
+        };
+
+      devShells.default = pkgs.callPackage ./devshell.nix { };
+    };
+
+  flake.nixosModules.default = import ./module.nix self;
+}