Although it is not intended to be used in this way, running `arc shell-complete` (without any arguments) outputs the following errors:
```
> arc shell-complete
[2014-05-20 08:39:13] ERROR 8: Undefined offset: 1 at [/home/joshua/dotfiles/modules/phabricator/arcanist/src/workflow/ArcanistShellCompleteWorkflow.php:102]
#0 ArcanistShellCompleteWorkflow::run() called at [/home/joshua/dotfiles/modules/phabricator/arcanist/scripts/arcanist.php:322]
[2014-05-20 08:39:13] ERROR 8: Undefined offset: 1 at [/home/joshua/dotfiles/modules/phabricator/arcanist/src/workflow/ArcanistShellCompleteWorkflow.php:105]
#0 ArcanistShellCompleteWorkflow::run() called at [/home/joshua/dotfiles/modules/phabricator/arcanist/scripts/arcanist.php:322]
```
Instead, we should output some sort of usage information.