gh-134360 Add processName attribute to logging.Formatter docstring (GH-134371)

Lib/logging/__init__.py

@@ -591,6 +591,7 @@ class Formatter(object):
     %(threadName)s      Thread name (if available)
     %(taskName)s        Task name (if available)
     %(process)d         Process ID (if available)
+    %(processName)s     Process name (if available)
     %(message)s         The result of record.getMessage(), computed just as
                         the record is emitted
     """