ft2-clone: install .desktop & icon

pkgs/by-name/ft/ft2-clone/package.nix

@@ -29,6 +29,17 @@ stdenv.mkDerivation (finalAttrs: {
     libiconv
   ];
 
+  postInstall = ''
+    install -Dm444 "$src/release/other/Freedesktop.org Resources/Fasttracker II clone.desktop" \
+      $out/share/applications/ft2-clone.desktop
+    install -Dm444 "$src/release/other/Freedesktop.org Resources/Fasttracker II clone.png" \
+      $out/share/icons/hicolor/512x512/apps/ft2-clone.png
+    # gtk-update-icon-cache does not like whitespace. Note that removing this
+    # will not make the build fail, but it will make the NixOS test fail.
+    substituteInPlace $out/share/applications/ft2-clone.desktop \
+      --replace-fail "Icon=Fasttracker II clone" Icon=ft2-clone
+  '';
+
   passthru.tests = {
     ft2-clone-starts = nixosTests.ft2-clone;
   };