LightGBM

[docs] Add LightGBM Tuner by Optuna links to README.md (#2893)

* Add LightGBM Tuner by Optuna links to README.md

* Removing Optuna Integrated badge

* Update README.md

Add repository code link.

* Update README.md

Co-authored-by: Nikita Titov <nekit94-08@mail.ru>