add more comment to readme file

README.md

@@ -101,7 +101,10 @@ cli:
     #            prop: propertyName
     #          flatten: true
     polymorphism:
+        # if true, polymorphism parameter with 'poly-resource' marked as true will be
+        # expanded into multiple operations for each subclasses
         expand-as-resource: true
+    # add hidden=true to all the parameters whose properties are all hidden or constant
     auto-parameter-hidden: false
     naming:
         cli: