Issue #12326: document the recommended idiom for checking sys.platform on Unix systems.
Also, point to the various alternatives.
diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index c412ee1..5c84e85 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -61,6 +61,13 @@
names have currently been registered: ``'posix'``, ``'nt'``, ``'mac'``,
``'os2'``, ``'ce'``, ``'java'``.
+ .. seealso::
+ :attr:`sys.platform` has a finer granularity. :func:`os.uname` gives
+ system-dependent version information.
+
+ The :mod:`platform` module provides detailed checks for the
+ system's identity.
+
.. _os-filenames: