Updated Documentation Part 2

I have proceeded with the install and am running: ```
RAILS_ENV=production bundle exec rake mastodon:setup
I have been just hitting enter for the default values shown greyed out answers are
PostgreSQL host: db
PostgreSQL port: 5432
Name of PostgreSQL database: postgres
Name of PostgreSQL user: postgres NOTE wondered if this should be mastodon
Password of PostgreSQL user (Unknown) supposed to not be used

dead in the water from at this point