Additional Documentation Examples

[bhamilton-at-ciq]

There were some sql features that I wanted to use that I had trouble figuring out the syntax for (specifically subqueries and IS NULL). They have didn't have clear examples in the godocs or the README.
But there were some very helpful examples in pika_psql_test.go. It would be nice if I could make those answers easier to find for the next person.

Would a PR adding more examples to the main README be appropriate?

[artarmstrong]

@mstg do you have a preference on this request?

[mstg]

Sorry for not responding quicker. My Github notifications are a mess. Would definitely appreciate a PR with more examples/docs