Issue #1370956 by greg.1.anderson, Rob Loach, msonnabaum: Added Support for commandfiles, alias files, and config files in DRUPA_ROOT/sites/all/drush.

Adding example command from Drupalcon Advanced Drush session http://chicago2011.drupal.org/sessions/advanced-drush

drush xkcd:
A command line tool (1) for a web site tool (2), that emulates
(badly) a web based tool (3) that emulates (badly) a command line tool (4) to
access a web site (5) with awesome geek humor.\n
(1) Drush
(2) Drupal
(3) http://uni.xkcd.com/
(4) BASH
(5) http://xkcd.com/