Closes #24060: Merged documentation update from 3.4.

Doc/library/logging.rst

@@ -486,7 +486,9 @@ Formatter Objects
 responsible for converting a :class:`LogRecord` to (usually) a string which can
 be interpreted by either a human or an external system. The base
 :class:`Formatter` allows a formatting string to be specified. If none is
-supplied, the default value of ``'%(message)s'`` is used.
+supplied, the default value of ``'%(message)s'`` is used, which just includes
+the message in the logging call. To have additional items of information in the
+formatted output (such as a timestamp), keep reading.
 
 A Formatter can be initialized with a format string which makes use of knowledge
 of the :class:`LogRecord` attributes - such as the default value mentioned above