The next time you push your changes into `<origin>` the changes will be automatically mirrored into `<mirror>`.~~
Forget the idea to use git hooks, first I forgot to make the hook executable and second it was the wrong type, instead of `post-commit` I had to use `pre-push`. Nonetheless, it won't work that way.
But, luckily there are is another apporach that is simply adding another push URL to the remote.