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.
props: Props,
    rootContainerInstance: Container,
    hostContext: HostContext,
    internalInstanceHandle: Object,
  ): Instance {
    let parentNamespace: string;
    if (__DEV__) {
      
      const hostContextDev = ((hostContext: any): HostContextDev);
      validateDOMNesting(type, null, null, hostContextDev.ancestorInfo);
      if (
        typeof props.children === 'string' ||
        typeof props.children === 'number'
      ) {
        const string = '' + props.children;
        const ownAncestorInfo = updatedAncestorInfo(
          hostContextDev.ancestorInfo,
          type,
          null,
        );
        validateDOMNesting(null, string, null, ownAncestorInfo);
      }
      parentNamespace = hostContextDev.namespace;
    } else {
      parentNamespace = ((hostContext: any): HostContextProd);
    }
    const domElement: Instance = createElement(
      type,
      props,
      rootContainerInstance,