message: Update React installation instructions
  We are using `Notifier` instead of `Airbrake.Notifier` since
diff: To report errors from a React app, you'll need to set up and use an
  [`ErrorBoundary` component](https://reactjs.org/blog/2017/07/26/error-handling-in-react-16.html)
  -and initialize an `Airbrake.Notifier` with your `projectId` and `projectKey`.
  +and initialize a `Notifier` with your `projectId` and `projectKey`.
  ```js
  import { Notifier } from '@airbrake/browser';
  