Doc: Add a link from enumeration basic type to enum attributes

Change-Id: I7a7c095f3df11233029e91b3a95262122ae31fcc
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

src/qml/doc/src/qmllanguageref/typesystem/basictypes.qdoc

@@ -673,4 +673,5 @@ property is only invoked when the property is reassigned to a different object v
     \endqml
 
     \sa {QML Basic Types}
+    \sa {qtqml-syntax-objectattributes.html#enumeration-attributes}{Enumeration Attributes}
 */