update app readme for setup instructions, since we're breaking away from the sqlite3 default. we COULD keep it, but it is generally better to use the same DB in dev as you use in production. 

In general, readme should cover the stack requirements and related instructions for specific setup. Otherwise new developers will have to guess at what they need to get it going. And being the guy to always write documentation isn't a bad thing, either. It helps with onramping or reramping if you drop it for a while.