feat: add contribute instruction

CONTRIBUTING.md

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+# How to Contribute / 如何贡献代码
+
+[English](#English)  
+[简体中文](#简体中文)
+
+## English
+
+### Pull Requests
+
+1. Fork the this repository
+2. Create a new branch for each feature or improvement
+3. Send a pull request from each feature branch against the dev branch.
+
+It is very important to separate new features or improvements into separate feature branches, and to send a
+pull request for each branch. This allows each feature or improvement to be reviewed and merged individually.
+
+### Coding Style
+
+All pull requests and commits **must** adhere to the [PSR-2 standard](https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-2-coding-style-guide.md) at least.
+And we **recommend** adhering to the [PSR-12 standard](https://github.com/php-fig/fig-standards/blob/master/proposed/extended-coding-style-guide.md).
+
+### Commit message
+
+The Commit message **must** containe all the changes you maked in sort.
+Please **do not** use words like "fix", "improve" only.
+
+## 简体中文
+
+### Pull Request
+
+1. Fork 本项目
+2. 为每一项新特性或改进创建一个新的分支
+3. 为每一项新特性或改进创建一个独立的 Pull Request 至 dev 分支
+
+我们建议你将不同的新特性置于不同的分支并以不同的 Pull Request 提交，这将有利于我们独立审查代码并独立合并。
+
+### 代码风格
+
+所有的 Pull request 和 commit 都至少**必须**遵守 [PSR-2 标准](https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-2-coding-style-guide.md)。
+我们建议**最好**遵守 [PSR-12 标准](https://github.com/php-fig/fig-standards/blob/master/proposed/extended-coding-style-guide.md)。
+
+### Commit 消息
+
+Commit 消息必须简洁地包含你所有的修改。请不要仅使用「修复」、「改进」等字样。