[docs] [issue37908] Add some examples of ArgumentParser.exit()

[hai shi]

Change by hai shi <shihai1991 at 126.com>:


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keywords: +patch
pull_requests: +15150
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/15455

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue37908>
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