Add msvcrt and winsound

Author: StanFromIreland

Doc/library/msvcrt.rst

@@ -22,6 +22,8 @@ api. The normal API deals only with ASCII characters and is of limited use
 for internationalized applications. The wide char API should be used where
 ever possible.
 
+.. availability:: Windows.
+
 .. versionchanged:: 3.3
    Operations in this module now raise :exc:`OSError` where :exc:`IOError`
    was raised.

Doc/library/winsound.rst

@@ -13,6 +13,8 @@
 The :mod:`winsound` module provides access to the basic sound-playing machinery
 provided by Windows platforms.  It includes functions and several constants.
 
+.. availability:: Windows.
+
 
 .. function:: Beep(frequency, duration)