flake.nix: fix the package

flake.nix

@@ -29,9 +29,11 @@
           }).overrideAttrs (oa:
             let
               inherit (nixpkgs.legacyPackages.${system})
+                pkg-config makeWrapper
                 copyDesktopItems makeDesktopItem;
             in {
               nativeBuildInputs = oa.nativeBuildInputs ++ [
+                pkg-config makeWrapper
                 nixpkgs.legacyPackages.${system}.copyDesktopItems
               ];
               desktopItems = [ (makeDesktopItem {
@@ -40,6 +42,14 @@
                 categories = [ "Game" ];
                 exec = "tracer";
               }) ];
+              installPhase = ''
+                ${oa.installPhase}
+
+                mkdir -p $out/share/tracer
+                cp -r assets $out/share/tracer/assets
+                wrapProgram $out/bin/tracer-game \
+                  --chdir $out/share/tracer
+              '';
             });
 
         defaultPackage = self.packages.${system}.${packageName};