Updated env instructions based on PostgreSQL issues

@mathemagica Can you please review these env instructions changes?
Ah, gotcha. Yeah, i guess the key thing is that your local env wont work at all if your db isnt running and your app can connect to it, so you can verify that your app is connecting to your db in a variety of ways: trying to drop and recreate your db, running your server, running rake db:migrate, etc.