Refactor flutter to support Android (#1072)

flutter/notes.md

@@ -0,0 +1,34 @@
+# Introduction
+
+This file keeps some notes about how packages in this directory
+are created.
+
+1. Create `sherpa_onnx`.
+
+```bash
+flutter create --template plugin sherpa_onnx
+```
+
+2. Create `sherpa_onnx_macos`
+
+```bash
+flutter create --template plugin_ffi --platforms macos sherpa_onnx_macos
+```
+
+3. Create `sherpa_onnx_linux
+
+```bash
+flutter create --template plugin_ffi --platforms linux sherpa_onnx_linux
+```
+
+4. Create `sherpa_onnx_windows
+
+```bash
+flutter create --template plugin_ffi --platforms linux sherpa_onnx_windows
+```
+
+5. Create `sherpa_onnx_android
+
+```bash
+flutter create --template plugin_ffi --platforms android --org com.k2fsa.sherpa.onnx sherpa_onnx_android
+```