Adding another C# client for the APIs (#250)

Hi great work putting this API together! :)

I've added another C# client for consuming the APIs based on the latest v2 contracts with support for all data types that should make it easier for any C# developers (.NET standard / core / framework) to use the API.

Author: degant

README.md

@@ -367,6 +367,7 @@ These are the available API wrappers created by the community. They are not nece
 
 * [CovidSharp by @Abdirahiim](https://github.com/Abdirahiim/covidtrackerapiwrapper)
 * [Covid19Tracker.NET by @egbakou](https://github.com/egbakou/Covid19Tracker.NET)
+* [CovidDotNet by @degant](https://github.com/degant/CovidDotNet)
 
 ### Python