Improve documentation for QML Effect types

The documentation should be more helpful in how to apply effects.

One of the first hits for me when searching for 'Qt 6 blur effect' is https://doc.qt.io/qt-6/qml-qtquick3d-effects-blur.html . Anyhow, it gives me little more than the information that it has an 'amount' property. In particular, no way to see how to apply the effect to anything.

Suggestions for improvements:

• Emphasize in the description that it is a blur effect for 3D
• Give minimal example of usage, or link to example