Added since badge

Author: JKorf

README.md

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 # ![.Binance.Net](https://raw.githubusercontent.com/JKorf/Binance.Net/master/Binance.Net/Icon/icon.png) Binance.Net  
 
-[![.NET](https://img.shields.io/github/actions/workflow/status/JKorf/Binance.Net/dotnet.yml?style=for-the-badge)](https://github.com/JKorf/Binance.Net/actions/workflows/dotnet.yml) ![License](https://img.shields.io/github/license/JKorf/Binance.Net?style=for-the-badge)
+[![.NET](https://img.shields.io/github/actions/workflow/status/JKorf/Binance.Net/dotnet.yml?style=for-the-badge)](https://github.com/JKorf/Binance.Net/actions/workflows/dotnet.yml) ![License](https://img.shields.io/github/license/JKorf/Binance.Net?style=for-the-badge) ![Since](https://img.shields.io/badge/since-2017-brightgreen?style=for-the-badge
+)
 
 Binance.Net is a strongly typed client library for accessing the [Binance REST and Websocket API](https://binance-docs.github.io/apidocs/#change-log).