Update documentation for D3045

Summary: Some minor updates for changes in D3045 and clarity.

Test Plan: Read documentation.

Reviewers: dschleimer, bos, btrahan, vrana

Reviewed By: dschleimer

CC: aran, cbiesinger

Maniphest Tasks: T1507, T1546

Differential Revision: https://secure.phabricator.com/D3046