Add example on how to use with faker (or equivalent)

[zhouzi]

Using this package with faker to generate realistic mocks should be straightforward. But it's such a common use case that I think it would be great to add an example for it.

I have not tried it but it should boil down to:

1. Use graphql-codegen's add plugin to prepend import { faker } from '@faker-js/faker'; to the generated files.
2. Define the scalars' defaults to use faker:

    scalarDefaults:
      ID: faker.random.alphaNumeric(16)
      Email: faker.internet.email()