(MODULES-11053) Add a note about the contains method

Author: DavidS

lib/puppet/type/anchor.rb

@@ -5,6 +5,8 @@
   @summary
     A simple resource type intended to be used as an anchor in a composite class.
 
+  > Note: this has been replaced by core puppet `contain()` method. Please see https://puppet.com/docs/puppet/latest/lang_containment.html for more information.
+
   In Puppet 2.6, when a class declares another class, the resources in the
   interior class are not contained by the exterior class. This interacts badly
   with the pattern of composing complex modules from smaller classes, as it