package.json not showing npm alternative

[yishengjiang99]

come on, facebook, you are so good at providing non-discriminating instructions on every guide you put online, so that us npm foks don't feel left out. then i check out this diff and it's only yarn!1

    "start": "yarn run relay; concurrently --kill-others --names \"react-scripts,relay\" \"react-scripts start\" \"yarn run relay --watch\"",
    "build": "yarn run relay && react-scripts build",