Mention potential breaking change to Kotlin DSL IDE resolver

Signed-off-by: Paul Merlin <paul@gradle.com>

subprojects/docs/src/docs/userguide/upgrading_version_5.adoc

@@ -139,6 +139,11 @@ The abstrace method `compile()` is no longer declared by `AbstractCompile`.
 Tasks extending `AbstractCompile` can implement their own `@TaskAction` method with the name of their choosing.
 They are also free to add a `@TaskAction` method with an `InputChanges` parameter without having to implement a parameter-less one as well.
 
+==== Kotlin DSL IDE support now requires Kotlin IntelliJ Plugin >= 1.3.50
+
+With Kotlin IntelliJ plugin versions prior to 1.3.50, Kotlin DSL scripts will be wrongly highlighted when the _Gradle JVM_ is set to a version different from the one in _Project SDK_.
+Simply upgrade your IDE plugin to a version >= 1.3.50 to restore the correct Kotlin DSL script highlighting behavior.
+
 ==== Updates to bundled Gradle dependencies
 
 - Groovy has been updated to http://groovy-lang.org/changelogs/changelog-2.5.8.html[Groovy 2.5.8].