Outdated note: the process is a lot easier now: after you brew install postgresql you can initialize or stop the daemon with these commands: brew services start postgresql or brew services stop postgresql.
new out put may look like
To have launchd start postgresql now and restart at login:
brew services start postgresql
Or, if you don't want/need a background service you can just run:
pg_ctl -D /usr/local/var/postgres start