Add VAD example for Dart API (#996)

dart-api-examples/README.md

@@ -0,0 +1,18 @@
+# Introduction
+
+This directory contains examples for Dart API.
+
+You can find the package at
+https://pub.dev/packages/sherpa_onnx
+
+## How to create an example in this folder
+
+```bash
+dart create vad
+cd vad
+
+# Edit pubspec.yaml and add sherpa_onnx to dependencies
+
+dart pub get
+dart run
+```