参数中有中括号和尖括号，我们要识别以下区别：
[] ：可选项
<>：必选项
初始化一个新的项目
yarn init
添加一个依赖包
yarn add [package]
yarn add [package]@[version]
yarn add [package]@[tag]
更新一个依赖包
yarn upgrade [package]
yarn upgrade [package]@[version]
yarn upgrade [package]@[tag]
删除一个依赖包
yarn remove [package]
安装所有的依赖包
yarn
or
yarn install
