Update help text on tools/modules/update.sh to be runnable from commandline.
Update help text on tools/modules/update.sh to be runnable from commandline.

Summary: This time without all of the random java refactoring rolled into the same arc land.

Reviewers: zarko, schroederc

Reviewed By: schroederc

Subscribers: #core_team

Differential Revision: https://phabricator-dot-kythe-repo.appspot.com/D1778

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