Add NuGet shield on the readme

README.md

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-#About [![Build status](https://ci.appveyor.com/api/projects/status/4uskxl4dm06fk3b9/branch/master?svg=true)](https://ci.appveyor.com/project/TechABC/zebus/branch/master)
+#About [![AppVeyor branch](https://img.shields.io/appveyor/ci/TechAbc/Zebus/master.svg)](https://ci.appveyor.com/project/TechABC/zebus) [![NuGet](https://img.shields.io/nuget/dt/Zebus.svg)](http://www.nuget.org/packages/Zebus/)
 
 Zebus is a lightweight peer to peer service bus, built with [CQRS](http://martinfowler.com/bliki/CQRS.html) principles in mind. It allows applications to communicate with each other in a fast and easy manner. Most of the complexity is hidden in the library and you can focus on writing code that matters to you, not debugging messaging code.