DOC:Use of "Yields" for documentation of DataFrame.iteritems()
changed `Returns` to `Yields`

closes #27860
@datapythonista @WillAyd : The fix looks good, but the documentation checks seem to be failing. See the also the discussion on the issue: https://github.com/pandas-dev/pandas/issues/27860. Someone will need to understand why the docstring validation sees iteritems and items differently Ah, it is because `iteritems` does `return self.items()` to do the same, therefore the docstring validation sees 'return' and thinks it needs to return something. See logic in 

https://github.com/pandas-dev/pandas/blob/master/scripts/validate_docstrings.py#L529-L562

That's of course a bit brittle. @datapythonista I suppose the easiest here is to ignore that rule? 
But currently we can only fully ignore a rule or not in code_checks ? Since we're Python 3 only now, my preference is to use `yield from self.items()` instead of `return self.items()`, and that should fix the doc validation I think. thanks @datapythonista that indeed seems a good idea Thanks @sameshl ! Glad to help! @jorisvandenbossche 