[Doc only] Code Review Request RT-30404: [FX3D] Need better documentation for the default PointLight

[Chien Yang]

Hi Kevin,

     Please review this simple javadoc change:

JIRA: https://javafx-jira.kenai.com/browse/RT-30404
Webrev: http://cr.openjdk.java.net/~ckyang/RT-30404/webrev.00/

Thanks,
- Chien