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.
parentComponent: ?ReactComponent<any, any, any>,
  children: ReactNodeList,
  container: DOMContainer,
  forceHydrate: boolean,
  callback: ?Function,
) {
  invariant(
    isValidContainer(container),
    'Target container is not a DOM element.',
  );
  if (__DEV__) {
    if (container._reactRootContainer && container.nodeType !== COMMENT_NODE) {
      const hostInstance = DOMRenderer.findHostInstanceWithNoPortals(
        container._reactRootContainer.current,
      );
      if (hostInstance) {
        warning(
          hostInstance.parentNode === container,
          'render(...): It looks like the React-rendered content of this ' +
            'container was removed without using React. This is not ' +
            'supported and will cause errors. Instead, call ' +