Add (or document?) Linux to MacOS Cross Building

On the [cross-building page](https://docs.conan.io/en/latest/systems_cross_building/cross_building.html#cross-building-with-conan) there's Linux to Windows, Linux to Android, and Linux to iOS... but there's no Linux to MacOS. AFAIK, iOS and MacOS are not the same (but I don't use Apple products (despite wanting to deploy to them)). idk if the functionality exists in conan or if it just needs to be documented.