Refactor C# code and support building nuget packages for cross-platforms (#144)

scripts/dotnet/README.md

@@ -0,0 +1,17 @@
+# Introduction
+
+[sherpa-onnx](https://github.com/k2-fsa/sherpa-onnx) is an open-source
+real-time speech recognition toolkit developed
+by the Next-gen Kaldi team.
+
+It supports streaming recognition on a variety of
+platforms such as Android, iOS, Raspberry, Linux, Windows, macOS, etc.
+
+It does not require Internet connection during recognition.
+
+See the documentation https://k2-fsa.github.io/sherpa/onnx/index.html
+for details.
+
+Please see
+https://github.com/k2-fsa/sherpa-onnx/tree/dot-net/dotnet-examples
+for how to use C# APIs of this package.