Updated .net version to 5.0

Author: mayavijx

c_sharp/OpenVINO_EP/yolov3_object_detection/README.md

@@ -9,7 +9,7 @@ The source code for this sample is available [here](https://github.com/microsoft
 # How to build
 
 ## Prerequisites
-1. Install [.NET Core 3.1](https://dotnet.microsoft.com/download/dotnet-core/3.1) or higher for you OS (Mac, Windows or Linux).
+1. Install [.NET 5.0](https://dotnet.microsoft.com/download/dotnet/5.0) or higher for you OS (Mac, Windows or Linux).
 2. [The Intel<sup>®</sup> Distribution of OpenVINO toolkit](https://docs.openvinotoolkit.org/latest/index.html)
 3. Use any sample Image as input to the sample.
 4. Download the latest YOLOv3 model from the ONNX Model Zoo.