[9] Code Review Request For 8130675:Document that setting scene on stage changes stage size unless explicitly set

[Chien Yang]

Hi Kevin,

Please review this proposed doc fix:

JIRA:https://bugs.openjdk.java.net/browse/JDK-8130675
Webrev: http://cr.openjdk.java.net/~ckyang/JDK-8130675/webrev.00/

Thanks,
- Chien