[docs] [issue37908] Add an example of ArgumentParser.exit()

[hai shi]

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


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title: Add some examples of ArgumentParser.exit() -> Add an example of ArgumentParser.exit()
type:  -> resource usage

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