Write some basic "dealing with Conduit changes" documentation

Summary:
Ref T9980. No magic here, just write a little bit about how to find outdated callers. Update the technical doc.

Also:

• Fix an unrelated bug where you couldn't leave comments if an object had missing, required, custom fields.
• Restore the ConduitConnectionLog table so bin/storage adjust doesn't complain.

Test Plan: Read docs.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9980

Differential Revision: https://secure.phabricator.com/D14784