What section do you mean? bytearray is not mentioned anywhere in
http://docs.python.org/3.4/library/os.html.

I think the problem with just linking to the C API section is that it doesn't help people that are only using pure Python. You can't look at a Python object and tell whether it implements the buffer protocol or not. Therefore, I think it would be important to give at least a reference to memoryview as the Python equivalent of the buffer protocol.