Add brief summary of cards (fixes #351)

Author: kpshek

docs/specification/1.0.md

@@ -42,7 +42,7 @@ In CDS Hooks, a _CDS Service_ is a service that provides patient-specific recomm
 
 A _CDS Client_ or _EHR_ is an electronic health record, or other clinical information system that consumes decision support by calling CDS Services at specific points in the application's workflow called [hooks](#hooks). Each hook defines the _hook context_, contextual information available within the client and specific to the workflow. Each service advertises which hooks it supports and what [_prefetch data_](#providing-fhir-resources-to-a-cds-service) (information needed by the CDS Service to determine what decision support should be presented) it requires.
 
-Decision support is then returned to the CDS Client in the form of [cards](#cds-service-response), which the client displays to the end-user as part of their workflow. Cards may be informational, or they may provide suggestions that the user may accept or reject, or they may provide a [link](#link) to additional information or even launch a SMART-app when additional user interaction is required.
+Decision support is then returned to the CDS Client in the form of [cards](#cds-service-response), which the client MAY display to the end-user as part of their workflow. Cards may be informational, or they may provide suggestions that the user may accept or reject, or they may provide a [link](#link) to additional information or even launch a SMART-app when additional user interaction is required.
 
 ## Discovery
 
@@ -421,9 +421,11 @@ Below is an example `fhirAuthorization` parameter:
 
 For successful responses, CDS Services SHALL respond with a 200 HTTP response with an object containing a `cards` element as described below.
 
+Each card contains decision support from the CDS Service. Generally speaking, cards are intended for display to an end user. The data format of a card defines a very minimal set of required attributes with several more optional attributes to suite a variety of use cases. For instance, narrative informational decision support, actionable suggestions to modify data, and links to SMART apps.
+
 > Note that because the CDS client may be invoking multiple services from the same hook, there may be multiple responses related to the same information. This specification does not address these scenarios specifically; both CDS Services and CDS Clients should consider the implications of multiple CDS Services in their integrations.
 
-### Card Array
+### HTTP Response
 
 Field | Optionality | Type | Description
 ----- | ----- | ----- | --------