update react with npx create react app code example

Example 1: new create react app

npx create-react-app my-app
cd my-app
npm start
//Note:npx on the first line is not a typo — 
//it’s a package runner tool that comes with npm 5.2+.

Example 2: react create app

npx create-react-app my-app
cd my-app
npm start