R1:8797c3ad0b21

Partly update the .arcconfig documentation

Summary: This needs more updates after .arclint is ready to use, but should fix most of the biggest issues.

Test Plan: Generated and read it.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D8539