Make it clear module attributes are prepended, closes #872

Author: José Valim

lib/elixir/lib/module.ex

@@ -474,7 +474,8 @@ defmodule Module do
   When registering an attribute, two options can be given:
 
   * `:accumulate` - Several calls to the same attribute will
-    accumulate instead of override the previous one;
+    accumulate instead of override the previous one. New attributes
+    are always added to the top of the accumulated list.
 
   * `:persist` - The attribute will be persisted in the Erlang
     Abstract Format. Useful when interfacing with Erlang libraries.