setting up Create React App with ESLint

Two main reasons

being able to lint on save with editor of choice
being able to have a npm run lint command to for automated linting check of contributors eg
- git pre-commit and pre-push hooks
- use in continuos integration/deployment settings, eg for PR

install dev dependencies in package.json

  "devDependencies": {
    ...
    "eslint": "^5.4.0",
    "eslint-config-airbnb": "^17.1.0",
    "eslint-plugin-import": "^2.14.0",
    "eslint-plugin-jsx-a11y": "^6.1.1",
    "eslint-plugin-react": "^7.11.1",
    ...

Then in npm scripts add

"scripts": {
    ...
    "lint": "eslint --ignore-path .gitignore .",
    "lint-fix": "eslint --ignore-path .gitignore . --fix",
    ...

optionally you can add a .eslintignore if there's extra files/folder to exclude that are not in the .gitignore.