Help is available by running farbot -h:

Usage: ./farbot [-h] [-f config file] [-r action]
    -h             Print usage (this message)
    -f <config>    Use configuration file
    -r <action>    Execute <action>

Supported actions:
  release        Build all defined releases, build all packages, and build 
                         the network installation root
  package       Build all defined packages, and build the network installation 
                         root (requires a release build)
  install           Build the network installation root (requires package and release builds)

./farbot -f farbot.conf -r release

./farbot -f farbot.conf -r install