Mention Byte Buddy as cglib alternative in the documentation

Author: Vampire

docs/interaction_based_testing.adoc

@@ -539,8 +539,9 @@ is only meant for documentation purposes and doesn't carry any semantics.
 
 Besides interfaces, Spock also supports mocking of classes. Mocking classes works
 just like mocking interfaces; the only additional requirement is to put `cglib-nodep-2.2` or higher
-and `objenesis-1.2` or higher on the class path. If either of these libraries is missing from
-the class path, Spock will gently let you know.
+or `byte-buddy` on the class path. When using normal `Mock`s or `Stub`s or `Spy`s that are
+configured accordingly, it is also necessary to put `objenesis-1.2` or higher on the class path.
+If either of these libraries is missing from the class path, Spock will gently let you know.
 
 NOTE: Java 8 is only supported from CGLIB 3.2.0 onwards.