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 (rootContainerInstance.nodeType === DOCUMENT_NODE) {
      type = '#document';
      let root = (rootContainerInstance: any).documentElement;
      namespace = root ? root.namespaceURI : getChildNamespace(null, '');
    } else {
      const container: any = rootContainerInstance.nodeType === COMMENT_NODE
        ? rootContainerInstance.parentNode
        : rootContainerInstance;
      const ownNamespace = container.namespaceURI || null;
      type = container.tagName;
      namespace = getChildNamespace(ownNamespace, type);
    }
    if (__DEV__) {
      const validatedTag = type.toLowerCase();
      const ancestorInfo = updatedAncestorInfo(null, validatedTag, null);
      return {namespace, ancestorInfo};
    }
    return namespace;
  },
  getChildHostContext(
    parentHostContext: HostContext,
    type: string,