[docs] [issue35790] Correct the description of sys.exc_info() and add a code example

Change by Géry <gery.ogam@gmail.com>: ---------- nosy: +cheryl.sabella -eric.araujo, ezio.melotti, willingc title: Correct a statement about sys.exc_info() values restoration -> Correct the description of sys.exc_info() and add a code example type: -> enhancement versions: +Python 3.6, Python 3.8, Python 3.9 _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue35790> _______________________________________