React Native 使用Yarn， Yarn是Facebook提供的替代npm的工具，可以加速node模块的下载

1. 安装Yarn: 

npm install -g yarn react-native-cli

2. 设置国内镜像：

npm config set registry https://registry.npm.taobao.org --global

npm config set disturl https://npm.taobao.org/dist --global

3. 命令, 参考：https://blog.csdn.net/u013233097/article/details/78652728

react-native init projectname

npm install --> yarn

npm install --save react-navigation --> yarn add react-navigation