新版的create-react-app，如果你之前在电脑安装过全局create-react-app就会出现项目不全的问题
A template was not provided. This is likely because you're using an outdated version of create-react-app. Please note that global installs of create-react-app are no longer supported.
解决方案：
卸载
npm uninstall -g create-react-app
如果上面不能卸载可以用下面方法
yarn global remove create-react-app
卸载完，然后再用
npx create-react-app [project-name]
就可以了
