[docs] updated list of external repos in README (#1848)
[docs] updated list of external repos in README (#1848)

* updated external repos section in README

* added SHAP

henry0312/LightGBM,microsoft/LightGBM,henry0312/LightGBM,henry0312/LightGBM,microsoft/LightGBM,microsoft/LightGBM,henry0312/LightGBM,microsoft/LightGBM,microsoft/LightGBM,henry0312/LightGBM