Add tts play example for .Net. (#676)

It plays the generated audio via a speaker as it is generating.

dotnet-examples/README.md

@@ -6,4 +6,14 @@ Please refer to the documentation
 https://k2-fsa.github.io/sherpa/onnx/csharp-api/index.html
 for details.
 
+```bash
+dotnet new console -n offline-tts-play
+dotnet sln ./sherpa-onnx.sln add ./offline-tts-play
+```
+
+```bash
+dotnet nuget locals all --list
+dotnet nuget locals all --clear
+```
+
 [sherpa-onnx]: https://github.com/k2-fsa/sherpa-onnx