add note for custom package scanning

[SebastianKuehnau]

A customer had issues with adding his custom theme to his application. The reason was a missing whitelisted-packages definition because his custom theme was in another package and could not be found by the vaadin-maven-plugin.

A note on the documentation on the custom-theme-packaging page might be very helpful.

[vaadin-bot]

Thanks for using Vaadin! We appreciate helping us to have better documentation and we’ll take care of this as soon as possible.

[jouni]

What exactly should be added? Could you offer a code snippet what you need to add and where? I’m a complete beginner when it comes to Maven package whitelisting.