More linter's short description

Summary: Closes T9353. I think this makes all descriptions at least basically informative.

Test Plan: arc linters - I can now understand what each one is about.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: Korvin

Maniphest Tasks: T9353

Differential Revision: https://secure.phabricator.com/D14106