Add examples for bad-str-strip-call

doc/data/messages/b/bad-str-strip-call/bad.py

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+my_string = "Hello World"
+my_string.strip("Hello")  # [bad-str-strip-call]

doc/data/messages/b/bad-str-strip-call/details.rst

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+A common misconception is that ``str.strip('Hello')`` removes the *substring* ``'Hello'`` from the beginning and end of the string.
+This is **not**  the case.
+From the `documentation <https://docs.python.org/3/library/stdtypes.html?highlight=strip#str.strip>`_:
+
+> The chars argument is not a prefix or suffix; rather, all combinations of its values are stripped
+
+Duplicated characters in the ``str.strip`` call, besides not having any effect on the actual result, may indicate this misunderstanding.

doc/data/messages/b/bad-str-strip-call/good.py

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+my_string = "Hello World"
+my_string.strip("Helo")

doc/data/messages/b/bad-str-strip-call/related.rst

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+- Documentation: `str.strip([chars]) <https://docs.python.org/3/library/stdtypes.html?highlight=strip#str.strip>`_