Updated requirements documentation to Core 1.1.

Author: Whathecode

README.md

@@ -2,7 +2,10 @@
 
 This library contains highly reuseable classes and methods I find to be missing in the cross-platform standard library of .NET.
 
-**Requires**: To open the solution and project files, the latest Visual Studio 2017 RC is required ([released on December 12](https://www.visualstudio.com/en-us/news/releasenotes/vs2017-relnotes) at time of writing).
+**Requires**:
+
+- To open the solution and project files, the latest Visual Studio 2017 RC is required ([released on December 15](https://www.visualstudio.com/en-us/news/releasenotes/vs2017-relnotes) at time of writing).
+- The test project requires the [.NET Core 1.1 SDK](https://www.microsoft.com/net/download/core).
 
 Namespaces from the original library are followed as much as possible: