Mention that private variable annotations are mangled (#101)

(Implemented in http://bugs.python.org/issue28076, https://hg.python.org/cpython/rev/1c2a4f29e1ab.)

pep-0526.txt

@@ -384,16 +384,19 @@ evaluated::
 
 In addition, at the module or class level, if the item being annotated is a
 *simple name*, then it and the annotation will be stored in the
-``__annotations__`` attribute of that module or class as a dictionary mapping
-from names to evaluated annotations. Here is an example::
+``__annotations__`` attribute of that module or class (mangled if private)
+as a dictionary mapping from names to evaluated annotations.
+Here is an example::
 
   from typing import Dict
   class Player:
       ...
   players: Dict[str, Player]
+  __points: int
 
   print(__annotations__)
-  # prints: {'players': typing.Dict[str, __main__.Player]}
+  # prints: {'players': typing.Dict[str, __main__.Player],
+  #          '_Player__points': <class 'int'>}
 
 ``__annotations__`` is writable, so this is permitted::