Add skforecast to README.md

[JavierEscobarOrtiz]

Hello everyone,

Thanks for the repo! I am adding skforecast to enrich this list with a library for time series forecasting.

Skforecast is a Python library for time series forecasting using machine learning models. It works with any regressor compatible with the scikit-learn API, including popular options like LightGBM, XGBoost, CatBoost, Keras, and many others.

Thanks!

Javier

@JoaquinAmatRodrigo