[3.14] pythonGH-139946: Document argparse includes color codes when redirecting to stderr to file (python#142398)

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Author: savannahostrowski

Doc/library/argparse.rst

@@ -644,6 +644,13 @@ variables and terminal capabilities.  However, if ``color=False``, colored
 output is always disabled, even if environment variables like ``FORCE_COLOR``
 are set.
 
+.. note::
+
+   Error messages will include color codes when redirecting stderr to a
+   file. To avoid this, set the |NO_COLOR|_ or :envvar:`PYTHON_COLORS`
+   environment variable (for example,
+   ``NO_COLOR=1 python script.py 2> errors.txt``).
+
 .. versionadded:: 3.14