docs: add section 'How to Contribute'

README.md

@@ -353,3 +353,14 @@ import "github.com/duke-git/lancet/validator"
 - [IsStrongPassword](https://github.com/duke-git/lancet/blob/main/docs/validator.md#IsStrongPassword)
 - [IsUrl](https://github.com/duke-git/lancet/blob/main/docs/validator.md#IsUrl)
 - [IsWeakPassword](https://github.com/duke-git/lancet/blob/main/docs/validator.md#IsWeakPassword)
+  
+
+## How to Contribute
+
+I really appreciate any code commits which make lancet lib powerful. Please follow the rules below to create your pull request.
+
+1. Fork the repository.
+2. Create your feature branch.
+3. Commit your changes.
+4. Push to the branch
+5. Create new pull request.

README_zh-CN.md

@@ -357,3 +357,14 @@ import "github.com/duke-git/lancet/validator"
 - [IsStrongPassword](https://github.com/duke-git/lancet/blob/main/docs/validator_zh-CN.md#IsStrongPassword)
 - [IsUrl](https://github.com/duke-git/lancet/blob/main/docs/validator_zh-CN.md#IsUrl)
 - [IsWeakPassword](https://github.com/duke-git/lancet/blob/main/docs/validator_zh-CN.md#IsWeakPassword)
+
+
+## 如何贡献代码
+
+非常感激任何的代码提交以使lancet的功能越来越强大。创建pull request时请遵守以下规则。
+
+1. Fork lancet仓库。
+2. 创建自己的特性分支。
+3. 提交变更。
+4. Push分支。
+5. 创建新的pull request。