[3.12] [pprint]: Add docstring about PrettyPrinter.underscore_numbers parameter (pythonGH-112963) (python#113053)

[pprint]: Add docstring about `PrettyPrinter.underscore_numbers` parameter (pythonGH-112963)
(cherry picked from commit 2a3c37c)

Co-authored-by: Sequew <88668176+KrySeyt@users.noreply.github.com>
Co-authored-by: Kirill Podoprigora <kirill.bast9@mail.ru>

Author: 3 people

Lib/pprint.py

@@ -128,6 +128,9 @@ def __init__(self, indent=1, width=80, depth=None, stream=None, *,
         sort_dicts
             If true, dict keys are sorted.
 
+        underscore_numbers
+            If true, digit groups are separated with underscores.
+
         """
         indent = int(indent)
         width = int(width)