[doc] Update Parameters-Tuning.rst (#2896)
[doc] Update Parameters-Tuning.rst (#2896)

Add Optuna link for automated hyperparameter tuning.
henry0312/LightGBM,microsoft/LightGBM,henry0312/LightGBM,microsoft/LightGBM,henry0312/LightGBM,microsoft/LightGBM,henry0312/LightGBM,microsoft/LightGBM,microsoft/LightGBM,henry0312/LightGBM