message: add code style/linting docs, clean up installation instructions
diff: @@ -20,6 +20,57 @@ Build with:
  `npm run build`
  +To run `primer-react` locally when adding or updating components:
  +
  +1. Clone this repo: `$ git clone https://github.com/primer/primer-react.git`
  +1. Install dependencies: `npm install`
  +1. Run the dev app with: `npm start`
  +
  +Remember to build docs before publishing with: `npm run build`
  +
  +### Code Style
  +
  +We use the [React configuration](https://github.com/github/eslint-plugin-github/blob/master/lib/configs/react.js)
  +from [GitHub's eslint plugin](https://github.com/github/eslint-plugin-github)
  +to lint our JavaScript. To check your work before pushing, run:
  +
  +```
  +npm run lint
  +```
  +
  +Or, you can use [npx] to run eslint on one or more specific files:
  +
  +
  +```sh
  +# lint the component and the tests in src/__tests__
  +npx eslint src/**/MyComponent.js
  +```
  +
  +**Protip:** The [eslint `--fix` flag](https://eslint.org/docs/user-guide/command-line-interface#--fix)
  +can automatically fix most linting errors, such as those involving whitespace
  +or incorrect ordering of object keys and imports. You can fix those issues
  +across the entire project with:
  +
  +```sh
  +npm run lint -- --fix
  +```
  +
  +**Protip:** `npm run lint -- --quiet` (or `npx eslint --quiet ...`) will
  +suppress warnings so that you can focus on fixing errors.
  +
  +### Testing
  +
  +We test our components with [Jest](https://facebook.github.io/jest/) and
  +[react-test-renderer](https://reactjs.org/docs/test-renderer.html). You can run
  +the tests locally with `npm test` (or `npm t`). To run the tests as you work,
  +run Jest in watch mode with:
  +
  +```
  +npm t -- --watch
  +```
  +
  +See [`src/__tests__/example.js`](src/__tests__/example.js) for an
  +example of how we're testing our components.
  ## Principles
  