Add documentation how to play with graphiql

[javpet]

Expected Behavior

More documentation for the README how someone can play around with graphiql to create mock resources.

Current Behavior

We don't have documentation around it currently in the README.

Possible Solution

Adding documentation in the README.

[aonomike]

Hi @javpet there is a great tutorial from pragmatic studio here. You can have a look and let me know if that helps. Maybe we should link this to the README?