Update Documents Index README.md (dotnet#3289)

Added reference to ML Cookbook, Roadmap, API Reference Doc, Samples and related Infer.NET and NimbusML Repo Docs

Author: tauheedul

docs/README.md

@@ -14,9 +14,23 @@ Project Docs
 - [Strong Name Signing](https://github.com/dotnet/corefx/blob/master/Documentation/project-docs/strong-name-signing.md)
 - [Public Signing](https://github.com/dotnet/corefx/blob/master/Documentation/project-docs/public-signing.md)
 - [Project NuGet Dependencies](https://github.com/dotnet/buildtools/blob/master/Documentation/project-nuget-dependencies.md)
+- [ML.NET Roadmap](https://github.com/dotnet/machinelearning/blob/master/README.md)
+- [ML.NET Cookbook](code/MlNetCookBook.md)
+- [ML.NET API Reference Documentation](https://docs.microsoft.com/en-us/dotnet/api/?view=ml-dotnet)
 
 Building from Source
 ====================
 
 - [Building ML.NET on Linux and OS X](building/unix-instructions.md)
-- [Building ML.NET on Windows](building/windows-instructions.md)
+- [Building ML.NET on Windows](building/windows-instructions.md)
+
+Repo of Samples
+====================
+
+- [ML.NET Samples](https://github.com/dotnet/machinelearning-samples/blob/master/README.md)
+
+Extensions for ML.NET
+====================
+
+- [Infer.NET - Bayesian / Probabilistic inference for ML.NET](https://github.com/dotnet/infer/blob/master/README.md)
+- [NimbusML - Python bindings for ML.NET](https://github.com/Microsoft/NimbusML/blob/master/README.md)