Currently if React is not loaded, ReactDOM shows this:

<img width="664" alt="screen shot 2017-08-08 at 3 36 52 pm" src="https://user-images.githubusercontent.com/810438/29077217-784c7624-7c4f-11e7-88bc-b055407523a9.png">

We should throw a nicer error message in the entry point I think.
if (
    !foundDevTools &&
    ExecutionEnvironment.canUseDOM &&
    window.top === window.self
  ) {
    
    if (
      (navigator.userAgent.indexOf('Chrome') > -1 &&
        navigator.userAgent.indexOf('Edge') === -1) ||
      navigator.userAgent.indexOf('Firefox') > -1
    ) {
      const protocol = window.location.protocol;
      
      if (/^(https?|file):$/.test(protocol)) {
        console.info(
          '%cDownload the React DevTools ' +
            'for a better development experience: ' +
            'https://fb.me/react-devtools' +
            (protocol === 'file:'
              ? '\nYou might need to use a local HTTP server (instead of file://): ' +
                  'https://fb.me/react-devtools-faq'
              : ''),
          'font-weight:bold',
        );
      }
    }
  }
}
module.exports = ReactDOMFiber;