Update README.md

Author: dadul96

README.md

@@ -10,6 +10,7 @@ There is no installation required. Just download the **TCP_Server_Client_Tester.
 ### Built With
 * [Visual Studio 2019](https://visualstudio.microsoft.com/) - IDE used for programming
 * [.NET](https://dotnet.microsoft.com/download/dotnet-framework) - Framework version 4.7.2 used
+* [WPF](https://docs.microsoft.com/en-us/dotnet/framework/wpf/) - Framework used for creating the GUI
 * [TcpConnection_Lib](https://github.com/dadul96/TcpConnection_Lib) - C# library that contains the TCP connection handling
 
 ### Author