Conduit - document that ERR-CONDUIT-CORE is coming atchya

Summary: Fixes T6863. Seems like this belongs there?

Test Plan: loaded up an API in conduit console and saw the new error text

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T6863

Differential Revision: https://secure.phabricator.com/D11261