brew update ; brew install postgres
postgres -D /usr/local/var/postgres
createdb 'whoami'
psql
(optional) Configure DB to start on system boot:
mkdir -p ~/Library/LaunchAgents
ln -sfv /usr/local/opt/postgresql/*.plist ~/Library/LaunchAgents
launchctl load ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist
/usr/local/Cellar/postgresql/9.5.2/bin/createuser -s postgres