Add 'arc linters' to list available linters and status

Summary: Ref T2039. We're starting to get kind of a lot of linters; provide `arc linters` to help users review and understand them and construct `.arclint` files.

Test Plan: {F152205}

Reviewers: btrahan, joshuaspence

Reviewed By: btrahan, joshuaspence

Subscribers: epriestley

Maniphest Tasks: T2039

Differential Revision: https://secure.phabricator.com/D9041