PEP 561
According to PEP 561, we just need to add this file to mark the lib as typed.

I don't know if all the lib is typed, maybe we also need to do that before merging.

- [ ] tests passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them

Thanks for the PR but this approach is still being discussed in https://github.com/pandas-dev/pandas/issues/28142 and https://github.com/pandas-dev/pandas/issues/45253, and pandas is not fully typed yet, so those issues need addressing before we can move forward with this.

Closing, but feel free to engage in the discussion in those issues first to move this along!
