pkgs/kde: set meta.platforms

pkgs/kde/lib/mk-kde-derivation.nix

@@ -108,6 +108,9 @@ in
           homepage = "https://invent.kde.org/${projectInfo.${pname}.repo_path}";
           license = lib.filter (l: l != null) (map (l: licensesBySpdxId.${l}) licenseInfo.${pname});
           maintainers = lib.teams.qt-kde.members;
+          # Platforms are currently limited to what upstream tests in CI, but can be extended if
+          # there's interest.
+          platforms = lib.platforms.linux ++ lib.platforms.freebsd;
         }
         // meta;
     };