Add note indicating ecmascript is only for mocking. (#46)

Author: ddebrunner

rest/pagination/api.graphql

@@ -67,6 +67,8 @@ type Query {
       resultroot: "values[]"
 
       # Ecmascript (with empty endpoint) is used to mimic the response from a REST api.
+      # Note ECMAScript is only used to generate a mock response with customer objects and page number metadata,
+      # using @rest against a real endpoint would not typically require any ECMAScript.
       endpoint: "stepzen:empty"
       ecmascript: """
       function transformREST() {