docs: fix bootstrap command (#9099)

.github/CONTRIBUTING.md

@@ -18,7 +18,7 @@ It's welcomed to pull request, And there are some tips about that:
 
 - When in doubt, keep your pull requests small. To give a PR the best chance of getting accepted, don't bundle more than one feature or bug fix per pull request. It's always best to create two smaller PRs than one big one.
 
-- When adding new features or modifying existing, please attempt to include tests to confirm the new behaviour.
+- When adding new features or modifying existing, please attempt to include tests to confirm the new behavior.
 
 - Rebase before creating a PR to keep commit history clear.
 
@@ -31,9 +31,9 @@ git clone git@github.com:youzan/vant.git
 
 cd vant
 
-npm run bootstrap
+yarn
 
-npm run dev
+yarn dev
 
 # open http://localhost:8080
 ```

docs/markdown/contribution.zh-CN.md

@@ -24,16 +24,16 @@
 git clone git@github.com:youzan/vant.git
 
 # 安装依赖
-cd vant && npm run bootstrap
+cd vant && yarn
 
 # 进入开发模式，浏览器访问 http://localhost:8080
-npm run dev
+yarn dev
 ```
 
 ### 目录结构
 
 - 仓库的组件代码位于 src 下，每个组件一个文件夹
-- docs 目录下是文档网站的代码，本地开发时可以在目录下运行 npm run dev 开启文档网站
+- docs 目录下是文档网站的代码，本地开发时可以在目录下运行 `yarn dev` 开启文档网站
 
 项目主要目录如下：