Proposal for notes

@cheddar -- thoughts?
This documentation feels like a good description of how to interpret a `note` event, but I'm wondering if that's actually how we want the ingestion side to work.  I.e. I kinda worry that it's putting too much burden on the submitter to get things just right.

How do you feel about the ingestion automatically adjusting the times to line up with this if `reference` is set?  I.e. it will move `time` to `displayTime` and set `time` to be the timestamp of the event from `reference`?