Updated description of cut and qcut
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [x] A colleague of mine complained about the quality of the `cut` description. I took a chance to update the description of `cut` and `qcut`. If there are some suggestions to improve the description - please let me know.
