Added two examples to documentation of DataFrame.std 
- [x] closes part of  #44162

Added two examples to the documentation of DataFrame.std function so that users can understand how to use it with different delta degrees of freedom.
Thanks for all the hints, I'll be sure to run pre-commit next time. I opened another pull request #44226 where I used pre-commit before committing changes. This should resolve the problems with this pull request. in the future just push to the same branch to update the existing PR