Clarify the change of behaviour from 3.14 about parsing negative numbers

Author: ptim0626

Doc/library/argparse.rst

@@ -1624,6 +1624,11 @@ argument::
 See also :ref:`the argparse howto on ambiguous arguments <specifying-ambiguous-arguments>`
 for more details.
 
+   .. versionchanged:: 3.14
+      Negative numbers in scientific notation (e.g. ``-2.5e-6``), with
+      underscores (e.g. ``-1_234.5``) and complex numbers (e.g. ``-1.2e-3j``)
+      are recognized as negative numbers.
+
 .. _prefix-matching:
 
 Argument abbreviations (prefix matching)