Update README.md

Author: yeonjuan

README.md

@@ -3,3 +3,9 @@
 # TypeScript ESLint Demo
 
 An online demo for [typescript-eslint](https://github.com/typescript-eslint/typescript-eslint) plugin. - [🚀 Online Demo](https://yeonjuan.github.io/typescript-eslint-demo/)
+
+## Development
+
+* `npm run dev` : run webpack dev server on http:localhost:8080
+* `npm run format` : format code with prettier
+* `npm run test`: run test