We need documentation describing how to use the explainability features in ML.NET

We have some great explainability features in ML.NET, but they are hidden here and there. It would be great to have an explainability doc, similar to the [ML.NET Cookbook](https://github.com/dotnet/machinelearning/blob/master/docs/code/MlNetCookBook.md), that showed how to use these features and what they do.