Mention that TWEAK is a new feature

Author: moritz

doc/Language/objects.pod6

@@ -444,7 +444,7 @@ example above).
 
 After the C<BUILD> methods have been called, methods named C<TWEAK> are
 called, if they exist, again with all the named arguments that were passed
-to C<new>.
+to C<new>. (C<TWEAK> is a new feature in v6.d / Rakudo 2016.11)
 
 Due to the nature of the default behavior of C<BUILDALL> and custom C<BUILD>
 submethods, named arguments to the constructor C<new> derived from C<Mu> can
@@ -527,7 +527,7 @@ class MyClass {
 
 If all you need to do is checking things after the actual construction,
 or modify attributes after the object construction, writing a submethod
-C<TWEAK> is a good approach:
+C<TWEAK> is a good approach (available in v6.d / Rakudo 2016.11):
 
 =begin code
 class RectangleWithCachedArea {