Update doc for available lints

Summary:
- Mention many new linters now included.
- Basic description of .arclint + example
- Move Philosophy sections above Configuration sections.

Test Plan: compile with bin/diviner.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: joshuaspence, hach-que, epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9000