Updated the docstring for reset_index in frame.py
If not all levels are removed, the index is not reset to default integer values.

import pandas as pd

x = pd.Series(range(3), index=pd.MultiIndex.from_arrays([['a', 'b', 'c'], [1, 2, 3]], names=['letters', 'numbers']))

print(x.reset_index('numbers', drop=True))

- [ ] 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
- [ ] whatsnew entry

This pull request is stale because it has been open for thirty days with no activity. Please update or respond to this comment if you're still interested in working on this. doc string update looks ok, but can we add the example you have above in the Examples section to make this clear. can you merge master and update tto comments Thanks for the PR but appears to have gone stale. If interested in continuing, please merge master and address the comments and we can reopen 