Improve bin/lipsum UX

Summary: Ref T9156. This makes the UX a little more modern/standard/safe.

Test Plan:
```
epriestley@orbital ~/dev/phabricator $ ./bin/lipsum generate
Choose which type or types of test data you want to generate, or select "all".

      - Differential Revisions
      - Files
      - Maniphest Tasks
      - Pastes
      - Pholio Mocks
      - Projects
      - User Accounts
```

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9156

Differential Revision: https://secure.phabricator.com/D14873

scripts/lipsum/manage_lipsum.php

@@ -5,10 +5,10 @@ $root = dirname(dirname(dirname(__FILE__)));
 require_once $root.'/scripts/__init_script__.php';
 
 $args = new PhutilArgumentParser($argv);
-$args->setTagline(pht('manage lipsum'));
+$args->setTagline(pht('synthetic data generator'));
 $args->setSynopsis(<<<EOSYNOPSIS
 **lipsum** __command__ [__options__]
-    Manage Phabricator Test Data Generator.
+    Generate synthetic test data to make development easier.
 
 EOSYNOPSIS
   );