R1:66de16fbc48f

Diffusion import documentation update

Summary: Fixes T12761.

Test Plan: doitlive

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley

Maniphest Tasks: T12761

Differential Revision: https://secure.phabricator.com/D18023