Add example for selda-json

[seanhess]

Hi there, I've used Selda on several projects, and I can't figure out how to use selda-json from the documentation.

I have a data type with a field that is Map Text Int and I'd like to serialize it as a postgres JSONB type. If I was willing to store it as text I could serialize it manually, or create a newtype to do that, but I'd like to use JSONB if possible.

Can you direct me to an example or create one?

[tonyalaribe]

We’re you able to figure this out?

[seanhess]

Hey @tonyalaribe, I don’t remember for sure, but I don’t think I was able to figure it out.