client, server 를 동시에 돌리기 위함

npm init
npm install express --save
npm install nodemon --save-dev
npm install concurrently --save

# server/package.json 수정

"scripts": {
  "test": "echo \"Error: no test specified\" && exit 1",
  "start": "node index.js",
  "backend" : "nodemon index.js",
  "dev": "concurrently \"npm run backend\" \"npm run start --prefix ../client\""
},