[docs] [issue30004] in regex-howto, improve example on grouping

[Mandeep Bhutani]

Mandeep Bhutani <mandeep at keemail.me> added the comment:

Cristian, Serhiy: I've submitted a PR for this bug. 

Cristian: I apologize for misspelling your name in a prior post.

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue30004>
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