[docs] Add LightGBM Tuner by Optuna links to README.md

[Crissman]

Hi!

Optuna is a new hyperparameter optimization library, and we've written an tuner module for LightGBM to make it easy to use Optuna to search for good hyperparameter settings and prune unpromising trials. We're looking for ways to let users of LightGBM know this is available and thought a badge to show Optuna integration is available would be helpful along with a link to Optuna in the further readings section.

If there are other ways you would recommend reaching out to LightGBM users to let them know about Optuna, please let us know.

Thanks!

[guolinke]

Thanks @Crissman , it is wonderful.

BTW, may be you can add optuna link to our documents, like https://github.com/microsoft/LightGBM/blob/master/docs/Parameters-Tuning.rst and https://github.com/microsoft/LightGBM/blob/master/docs/Parameters.rst

[jameslamb]

Thanks @Crissman , it is wonderful.

BTW, may be you can add optuna link to our documents, like https://github.com/microsoft/LightGBM/blob/master/docs/Parameters-Tuning.rst and https://github.com/microsoft/LightGBM/blob/master/docs/Parameters.rst

I think it would be enough to just add to Parameters-Tuning.rst. In my opinion we should try to keep Parameters.rst limited to just telling you what parameters exist and the impact of choosing different values for them.

[jameslamb]

Thanks @Crissman !

[jameslamb]

thanks @Crissman !