Include NuGet download count

Author: drieseng

README.md

@@ -3,6 +3,7 @@ SSH.NET
 SSH.NET is a Secure Shell (SSH-2) library for .NET, optimized for parallelism.
 
 [![Version](https://img.shields.io/nuget/vpre/SSH.NET.svg)](https://www.nuget.org/packages/SSH.NET)
+[![NuGet download count](https://img.shields.io/nuget/dt/SSH.NET.svg)
 [![Build status](https://ci.appveyor.com/api/projects/status/ih77qu6tap3o92gu/branch/develop?svg=true)](https://ci.appveyor.com/api/projects/status/ih77qu6tap3o92gu/branch/develop)
 
 ## Introduction