Adding Chinese version of README (#46)

Author: 239573049

README.md

@@ -3,6 +3,7 @@
 ![nanoFramework logo](https://raw.githubusercontent.com/nanoframework/Home/main/resources/logo/nanoFramework-repo-logo.png)
 
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+document language: [English](README.md) | [简体中文](README.zh-cn.md)
 
 # Welcome to the .NET **nanoFramework** nanoFramework.Device.Bluetooth Library repository