Hello Adrian,
Thanks for pointing out this to us.
We indeed need to update this documentation. Meantime, you can follow our up-to-date example project where we have fixed issues with those files.
You can launch this project code by running the theme command.
import * as React from 'react'
import { PreviewStoreProvider } from 'gatsby-source-prismic'
export const wrapRootElement = ({ element }) => (
<PreviewStoreProvider initialEnabled={true}>{element}</PreviewStoreProvider>
)
Let me know if you have any doubt.
Thanks,
Priyanka