message: Add import and export for React example
  The general React library which is needed in this example. To use this
  example in your app, you also need to export the addition.
diff: @@ -5,6 +5,7 @@ To report errors from a React app, you'll need to set up and use an
  and initialize a `Notifier` with your `projectId` and `projectKey`.
  ```js
  +import React, { Component } from 'react';
  import { Notifier } from '@airbrake/browser';
  class ErrorBoundary extends React.Component {
  @@ -35,6 +36,8 @@ class ErrorBoundary extends React.Component {
  return this.props.children;
  }
  }
  +
  +export default ErrorBoundary;
  ```
  Then you can use it as a regular component:
  