Summary:
Ref T4843. Document the new assistive features in the developer docs.
(Also use the recommended mode to set them. They're equivalent for `aural=true` (but not for `aural=false`), so this doesn't actually change anything.)
Test Plan: Read documentation.
Reviewers: btrahan, chad
Reviewed By: chad
Subscribers: epriestley
Maniphest Tasks: T4843
Differential Revision: https://secure.phabricator.com/D8926
