[docs] [issue9182] document “--” as a way to distinguish option w/ narg='+' from positional argument in argparse

[Berker Peksag]

Changes by Berker Peksag <berker.peksag at gmail.com>:


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nosy: +berker.peksag

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue9182>
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