Up-to-date docs

The readme intro starts with this paragraph:

> The Reactive Extensions (Rx) is a library for composing asynchronous and event-based programs using observable sequences and LINQ-style query operators. Using Rx, developers *__represent__* asynchronous data streams with [Observables](https://docs.microsoft.com/dotnet/api/system.iobservable-1), *__query__* asynchronous data streams using [LINQ operators](http://msdn.microsoft.com/en-us/library/hh242983.aspx), and *__parameterize__* the concurrency in the asynchronous data streams using [Schedulers](http://msdn.microsoft.com/en-us/library/hh242963.aspx). Simply put, Rx = Observables + LINQ + Schedulers.

Two of the three links are to pages that have the notice, "We're no longer updating this content regularly." The doc path listed on each page is "Docs / Previous Versions / .NET / Reactive Extensions". Where should we confidently go to find up-to-date documentation on the current version of Reactive Extensions for .NET?