Add Nuget version badge

README.md

@@ -2,6 +2,7 @@ api.ai: .NET Core Library
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 [![Build Status](https://travis-ci.org/api-ai/api-ai-net.svg?branch=master)](https://travis-ci.org/api-ai/api-ai-net)
+[![Nuget Version](https://img.shields.io/nuget/v/ApiAiSDK.svg)](https://www.nuget.org/packages/ApiAiSDK/)
 
 The api.ai .NET Core Library makes it easy to integrate the [API.AI natural language processing API](http://api.ai) into your .NET application. API.AI allows using voice commands and integration with dialog scenarios defined for a particular agent in API.AI.