Document how to return JSON when accessed via JSON:API

Upon further inspection, the JSON:API Extras module has a field enhancer that can be used to return decoded JSON data from a JSON field.

1. Install JSON:API Extras.
2. Go to admin/config/services/jsonapi/resource_types/ and override the desired resource type.
3. For the JSON field, click Advanced.
4. Select JSON Field for the enhancer.

So since a major ecosystem contrib module already provides a way to do this, I think this issue can be closed.

Thanks for spotting that, ptmkenny. Let's document it somewhere.

Ok, how about adding it to the README?

I made some minor tweaks. Committed. Thank you.

Automatically closed - issue fixed for 2 weeks with no activity.