Add a synopsis and example for "arc help land"

Summary: Ref T13546. Small documentation fix. Mostly so I can have more things to land.

Test Plan: Ran "arc help land", saw help.

Maniphest Tasks: T13546

Differential Revision: https://secure.phabricator.com/D21321

src/workflow/ArcanistLandWorkflow.php

@@ -91,9 +91,9 @@ branch.
 EOTEXT
       );
 
-    // TODO: Add command synopses.
-
     return $this->newWorkflowInformation()
+      ->setSynopsis(pht('Publish reviewed changes.'))
+      ->addExample(pht('**land** [__options__] [__ref__ ...]'))
       ->setHelp($help);
   }