Was reading http://guides.rubyonrails.org/getting_started.html
Was reading about setting up postgresql. I'm using Postgres.app and
needed to add host: localhost in database.yml. Even though Postgres.app
has its own documentation that clearly notes this, I think it would be
nice to mention it on this doc page as well. The example is for the
development environment, so it's likely many people would want to use
host: localhost. Won't cry if this change is not accepted. I'm still
pretty new to Rails. [ci skip]