clarifying regex pipe behavior
[Current documentation for `pandas.Series.str.contains()`](https://pandas.pydata.org/pandas-docs/stable/generated/pandas.Series.str.contains.html) states that the `|` acts as a regex **and** operator ("Returning ‘house’ and ‘parrot’ within same string."), while I believe it is actually an **or** operator. I've updated the phrase and example to demonstrate this behavior in what I think is a clearer way, though I'm definitely open to suggestions to improve it further.

- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
