Update README.md

Author: mendozagit

README.md

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 # FiscalAPI SDK para .NET
-
+[![.NET](https://img.shields.io/badge/.NET-6.0-purple.svg)](https://dotnet.microsoft.com/download/dotnet/6.0)
+[![.NET](https://img.shields.io/badge/.NET-8.0-purple.svg)](https://dotnet.microsoft.com/download/dotnet/8.0)
+[![.NET](https://img.shields.io/badge/.NET-9.0-purple.svg)](https://dotnet.microsoft.com/download/dotnet/9.0)
 [![NuGet](https://img.shields.io/nuget/v/FiscalApi.svg)](https://www.nuget.org/packages/FiscalApi/)
 [![License](https://img.shields.io/github/license/FiscalAPI/fiscalapi-net)](https://github.com/FiscalAPI/fiscalapi-net/blob/master/LICENSE.txt)