Doc/library/os.rst: os.waitid absent on MacOS (#104558)

* Doc/library/os.rst: `os.waitid` absent on MacOS

Co-authored-by: AN Long <aisk@users.noreply.github.com>

Author: johnhawkinson

Doc/library/os.rst

@@ -4986,6 +4986,9 @@ written in Python, such as a mail server's external command delivery program.
 
    .. availability:: Unix, not Emscripten, not WASI.
 
+   .. note::
+      This function is not available on macOS.
+
    .. versionadded:: 3.3