Here's what I've added:

> *It is important to note that using the new method of `addPlugins` with `PlayJava` or `PlayScala` is incompatible with `playJavaSettings`, `playScalaSettings` or the use of `play.Project`. While the latter methods are deprecated they may still be used for the time being. However we strongly encourage you to adopt the `addPlugins` with `PlayJava` or `PlayScala` method.*