Document usage of custom ErrorReporter component

It would be great if there were some more documentation on how to use a local component as the ErrorReporter. I have been struggling with this for some time.

Using relative paths did not work, and setting a webpack alias did not seem to work either.

I get undefined as the value of ErrorReporter if I use a default export for the component:
`export default class AppError extends...`
And i get an empty object if using module.exports.
`module.exports = AppError`