[issue27992] Clarify %(prog)s in argparse help formatter returns basename of sys.argv[0] by default

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan <tir.karthi at gmail.com>:


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nosy: +rhettinger

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue27992>
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