Add .. availability:: Windows directive to COM-related function prototype (GH-127436)

Add a directive to prototype that "returns a foreign function that will call a COM method"

Author: junkmd

Doc/library/ctypes.rst

@@ -1812,6 +1812,8 @@ different ways, depending on the type and number of the parameters in the call:
    the COM interface as first argument, in addition to those parameters that
    are specified in the :attr:`!argtypes` tuple.
 
+   .. availability:: Windows
+
 
 The optional *paramflags* parameter creates foreign function wrappers with much
 more functionality than the features described above.