Inform the user about the fact that query builders implement Promise

[L-Mario564]

I had opened a discussion in the ORM repo about adding a feature that transforms the query's result after it's been obtained from the driver, but I had forgotten that this is already possible using the then method on the query builder, since it just extends Promise.

I feel like the fact that the query builders extend Promise is pretty easy to miss, and could be something worth noting in the documentation.

A frequently asked feature in the core API is some findFirst and findFirstOrThrow equivalent, and the documentation can provide an example as to how a developer than implement such functionality:

const user = db.select().from(users).limit(1).then((result) => result[0]);