Missing PShape::getChildren() method documentation

[HoloTheDrunk]

The PShape::getChildren() method is not documented but still accessible. Given how ubiquitous and idiomatic for-each loops are in Java, making it clear that the method is available would likely help beginners.

[etleyden]

The documentation on the website is generated from the source code, right? I can edit a javadoc comment here, but it is a separate repository.