Adding a helpful error message for "Could not connect"

[jwoertink]

Fixes #983

I just got bit by this again. If your default user is postgres, you generally already have a database called postgres; however, in the case of Avram specs, we use the user lucky. This means you have to have a local db call lucky in order to run lucky db.create. This is because when we removed the pg_client dependency we no longer have access to createdb. Instead, we have to connect to the DB server and run some SQL... but postgres doesn't let you connect to the server without being attached to some database.. 🐔 🥚 🤷‍♂️

This PR just adds an error message that tells you

▸ If this is your first run, create a database named 'lucky' that this same user will have access to

That should at least point to a common fix for this problem.