add boundaries section to DR:

Propose adding this text from Procedure :

"Note that many diagnostic processes are procedures that generate Observations and DiagnosticReports. In many cases, such an observation does not require an explicit representation of the procedure used to create the observation, but where there are details of interest about how the diagnostic procedure was performed, the procedure resource is used to describe the activity.

and this from Obsevation:

"In contrast to the Observation resource, the DiagnosticReport resource typically includes additional clinical context and and some mix of atomic results, images, imaging reports, textual and coded interpretation, and formatted representations. Laboratory reports, pathology reports, and imaging reports should be represented using the DiagnosticReport resource. The Observation resource is referenced by the DiagnosticReport to provide the atomic results for a particular investigation."

as well as paragraphs relating imaging and DO - TBD