Document that logging registers shutdown as an atexit handler (GH-12378)

diff --git a/Doc/library/logging.rst b/Doc/library/logging.rst
index 5adde29..08555c3 100644
--- a/Doc/library/logging.rst
+++ b/Doc/library/logging.rst
@@ -1215,6 +1215,10 @@
    closing all handlers. This should be called at application exit and no
    further use of the logging system should be made after this call.
 
+   When the logging module is imported, it registers this function as an exit
+   handler (see :mod:`atexit`), so normally there's no need to do that
+   manually.
+
 
 .. function:: setLoggerClass(klass)