[docs] Add link to Ray Tune in hyperparameters.rst (#2647)
[docs] Add link to Ray Tune in hyperparameters.rst (#2647)

Co-authored-by: Kai Fricke <31ea678c44dc4e8e22ccfd165592dd71a30e46ae@anyscale.com>
williamFalcon/pytorch-lightning,williamFalcon/pytorch-lightning