DOC: Add Notes about difference to numpy behaviour for ddof in std() GH35985
- [x] closes #35985
- [ ] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

> Thanks @timhunderwood
> 
> > normalizes by N
> 
> Are you sure this is correct? Does dividing by N actually normalise the quantity?
> 
> IMO it should be enough to write something like
> 
> ```
> Notes
> -----
> To have the same behaviour as `numpy.std`, use `ddof=0` (instead of the default `ddof=1`)
> ```



> Thanks @timhunderwood
> 
> > normalizes by N
> 
> Are you sure this is correct? Does dividing by N actually normalise the quantity?
> 
> IMO it should be enough to write something like
> 
> ```
> Notes
> -----
> To have the same behaviour as `numpy.std`, use `ddof=0` (instead of the default `ddof=1`)
> ```

thanks @MarcoGorelli , I agree this could be confusing. I've changed to your simpler wording, thanks. > Looks good to me, can you fetch and merge upstream/master and then push again to restart the CI process in order to get it green?

Done - CI process has started... Thanks @timhunderwood !