feat: add Nix flake

flake.nix

@@ -0,0 +1,38 @@
+{
+  description = "devshell for uad-ng";
+
+  inputs.flake-utils.url = "github:numtide/flake-utils";
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem
+      (system:
+        let pkgs = nixpkgs.legacyPackages.${system}; in
+        {
+          devShells.default = pkgs.mkShell {
+            packages = with pkgs;
+            [
+              rustc
+              cargo
+              clang
+              pkg-config
+              mold
+              expat
+              android-tools
+            ];
+
+            LD_LIBRARY_PATH = "${nixpkgs.lib.makeLibraryPath [
+              pkgs.fontconfig
+              pkgs.freetype
+              pkgs.libglvnd
+              pkgs.xorg.libX11
+              pkgs.xorg.libXcursor
+              pkgs.xorg.libXi
+              pkgs.xorg.libXrandr
+              pkgs.libxkbcommon
+              pkgs.wayland
+            ]}";
+            LIBCLANG_PATH="${pkgs.llvmPackages.libclang.lib}/lib";
+          };
+        }
+      );
+}