add: flake.nix and other required files for nix build

default.nix

@@ -0,0 +1,41 @@
+{ lib
+, fetchFromGitHub
+, buildGoModule
+}:
+buildGoModule rec {
+  pname = "clash-meta";
+  version = "1.13.1";
+
+  src = fetchFromGitHub {
+    owner = "MetaCubeX";
+    repo = "Clash.Meta";
+    rev = "1684756b79a232ee8f875bcfd87371f5c0ef066b";
+    sha256 = "sha256-7g/Wcll0w4EhPI+KodtLHINqaR2larQNnP9YAsgNiN4=";
+  };
+
+  vendorSha256 = "sha256-7HjYcoqWA5gvPUc5psCgy0UTc17CBzBJ/OiGvII/iBA=";
+
+  # Do not build testing suit
+  excludedPackages = [ "./test" ];
+
+  CGO_ENABLED = 0;
+
+  ldflags = [
+    "-s"
+    "-w"
+    "-X github.com/Dreamacro/clash/constant.Version=${version}"
+  ];
+
+  # network required
+  doCheck = false;
+
+  postInstall = ''
+    mv $out/bin/clash $out/bin/clash-meta
+  '';
+
+  meta = with lib; {
+    description = "Another Clash Kernel";
+    homepage = "https://github.com/MetaCubeX/Clash.Meta";
+    license = licenses.gpl3Only;
+  };
+}