docs: add links between Chinese and English version (#417)

Co-authored-by: rick <linuxsuren@users.noreply.github.com>

CONTRIBUTING-ZH.md

@@ -1,3 +1,5 @@
+> 中文 | [English](CONTRIBUTING.md)
+
 请加入我们，共同完善这个项目。
 
 后端由 [Golang](https://go.dev/) 编写，前端由 [Vue](https://vuejs.org/) 编写。

CONTRIBUTING.md

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+> English | [中文](CONTRIBUTING-ZH.md)
+
 Please join us to improve this project.
 
 The backend is written by [Golang](https://go.dev/), and the front-end is written by [Vue](https://vuejs.org/).

README-ZH.md

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 [![Docker Pulls](https://img.shields.io/docker/pulls/linuxsuren/api-testing)](https://hub.docker.com/r/linuxsuren/api-testing)
 [![LinuxSuRen/open-source-best-practice](https://img.shields.io/static/v1?label=OSBP&message=%E5%BC%80%E6%BA%90%E6%9C%80%E4%BD%B3%E5%AE%9E%E8%B7%B5&color=blue)](https://github.com/LinuxSuRen/open-source-best-practice)
 
+> 中文 | [English](README.md)
+
 一个开源的 API 测试工具。🚀
 
 ## 功能特性

README.md

@@ -5,6 +5,8 @@
 [![Docker Pulls](https://img.shields.io/docker/pulls/linuxsuren/api-testing)](https://hub.docker.com/r/linuxsuren/api-testing)
 [![LinuxSuRen/open-source-best-practice](https://img.shields.io/static/v1?label=OSBP&message=%E5%BC%80%E6%BA%90%E6%9C%80%E4%BD%B3%E5%AE%9E%E8%B7%B5&color=blue)](https://github.com/LinuxSuRen/open-source-best-practice)
 
+> English | [中文](README-ZH.md)
+
 This is a API testing tool. 🚀
 
 ## Features