minor clarification for operationId usage in link objects (OAI#1733)

* minor clarification

it's a bit confusing that both the id and the reference are called "operationId", so this tweak makes the text a bit more explicit.

* use right terminology

Co-Authored-By: Mike Ralphson <mike.ralphson@gmail.com>

Co-authored-by: Ron <ron@swagger.io>
Co-authored-by: Mike Ralphson <mike.ralphson@gmail.com>
Signed-off-by: Mike Ralphson <mike.ralphson@gmail.com>

versions/3.1.0.md

@@ -2123,7 +2123,7 @@ solely by the existence of a relationship.
 ##### OperationRef Examples
 
 As references to `operationId` MAY NOT be possible (the `operationId` is an optional 
-value), references MAY also be made through a relative `operationRef`:
+field in an [Operation Object](#operationObject)), references MAY also be made through a relative `operationRef`:
 
 ```yaml
 links: