Minor update to Discovery documentation (#386) (Fixes #303)

Clarify that the Discovery endpoint shall include a description, not the purpose of the CDS service

Author: isaacvetter

docs/specification/1.0.md

@@ -25,7 +25,7 @@ CDS Hooks implementers are not required to use the Open API Specification interf
 
 ## Discovery
 
-Developers of CDS Services SHALL provide a stable endpoint for allowing EHRs to discover available CDS Services, including information such as the purpose of the CDS Service, when it should be invoked, and any data that is requested to be prefetched.
+Developers of CDS Services SHALL provide a stable endpoint for allowing EHRs to discover available CDS Services, including information such as a description of the CDS Service, when it should be invoked, and any data that is requested to be prefetched.
 
 A CDS Service provider SHALL expose its Discovery endpoint at"