Fixes #14864: Added documentation on how to undo the effects of a logging.disable() call.

Doc/library/logging.rst

@@ -942,7 +942,8 @@ functions.
    effect is to disable all logging calls of severity *lvl* and below, so that
    if you call it with a value of INFO, then all INFO and DEBUG events would be
    discarded, whereas those of severity WARNING and above would be processed
-   according to the logger's effective level.
+   according to the logger's effective level. To undo the effect of a call to
+   ``logging.disable(lvl)``, call ``logging.disable(logging.NOTSET)``.
 
 
 .. function:: addLevelName(lvl, levelName)