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 (!isValidElement(element)) {
        if (typeof element === 'string') {
          invariant(
            false,
            'ReactDOM.render(): Invalid component element. Instead of ' +
              "passing a string like 'div', pass " +
              "React.createElement('div') or <div />.",
          );
        } else if (typeof element === 'function') {
          invariant(
            false,
            'ReactDOM.render(): Invalid component element. Instead of ' +
              'passing a class like Foo, pass React.createElement(Foo) ' +
              'or <Foo />.',