Merge pull request #2372 from davidsh/readme_update

Add System.Net.WebHeaderCollection to README.md

Author: davidsh

README.md

@@ -92,6 +92,7 @@ More libraries are coming soon (the overall list of items we currently plan to m
 |<sub>**System.Linq.Queryable**<br/>[![MyGet Package](https://img.shields.io/myget/dotnet-core/v/System.Linq.Queryable.svg)](https://www.myget.org/gallery/dotnet-core)</sub>|<sub>Provides LINQ standard query operators that operate on objects that implement ```IQueryable<T>```.</sub>|
 |<sub>**System.Net.Http**<br/>[![MyGet Package](https://img.shields.io/myget/dotnet-core/v/System.Net.Http.svg)](https://www.myget.org/gallery/dotnet-core)</sub>|<sub>Provides a programming interface for modern HTTP applications, including HTTP client components that allow applications to consume web services over HTTP and HTTP components that can be used by both clients and servers for parsing HTTP headers.</sub>|
 |<sub>**System.Net.Http.WinHttpHandler**<br/>[![MyGet Package](https://img.shields.io/myget/dotnet-core/v/System.Net.Http.WinHttpHandler.svg)](https://www.myget.org/gallery/dotnet-core)</sub>|<sub>Provides a message handler for HttpClient based on the WinHTTP interface of Windows. While similar to HttpClientHandler, it provides developers more granular control over the application's HTTP communication than the HttpClientHandler.</sub>|
+|<sub>**System.Net.WebHeaderCollection**<br/>[![MyGet Package](https://img.shields.io/myget/dotnet-core/v/System.Net.WebHeaderCollection.svg)](https://www.myget.org/gallery/dotnet-core)</sub>|<sub>Contains types that represent HTTP request and response headers. This library is used with classes such as System.Net.HttpWebRequest and System.Net.HttpWebResponse and allows developers to query/edit header names/values.</sub>|
 |<sub>**System.Numerics.Vectors**<br/>[![MyGet Package](https://img.shields.io/nuget/vpre/System.Numerics.Vectors.svg)](http://www.nuget.org/packages/System.Numerics.Vectors/)</sub>|<sub>Provides a set of basic vector types that leverage single instruction, multiple data (SIMD) CPU instructions.</sub>|
 |<sub>**System.ObjectModel**<br/>[![MyGet Package](https://img.shields.io/myget/dotnet-core/v/System.ObjectModel.svg)](https://www.myget.org/gallery/dotnet-core)</sub>|<sub>Provides types and interfaces that enable the creation of observable types that provide notifications to clients when changes are made.</sub>|
 |<sub>**System.Reflection**<br/>[![MyGet Package](https://img.shields.io/myget/dotnet-core/v/System.Reflection.svg)](https://www.myget.org/gallery/dotnet-core)</sub>|<sub>Provides types that retrieve information about assemblies, modules, members, parameters, and other entities in managed code by examining their metadata.</sub>|