docs: add language switcher to README

Author: sunbird89629

README.md

@@ -1,5 +1,7 @@
 # Http Inspector
 
+**Language**: **English** · [简体中文](README_zh.md)
+
 [![pub.dev](https://img.shields.io/pub/v/http_inspector.svg)](https://pub.dev/packages/http_inspector)
 [![License: MIT](https://img.shields.io/badge/license-MIT-blue.svg)](LICENSE)
 [![Flutter](https://img.shields.io/badge/Flutter-%3E%3D3.0.5-02569B?logo=flutter)](https://flutter.dev)