Summary: Fixes T2605. Provide some instructions on configuring RDS properly. The "DB Parameter Group" thing in the web UI seems pretty easy to use, it's just not obvious that it's what you should be using.
Test Plan: Jiggled these warnings to trigger them, viewed the output, saw a table of values and a hint about RDS.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T2605
Differential Revision: https://secure.phabricator.com/D10343
