DOC: tz_convert docs could be improved for Series and DataFrame

[jackgoldsmith4]

Pandas version checks

• I have checked that the issue still exists on the latest versions of the docs on main here

Location of the documentation

https://pandas.pydata.org/docs/reference/api/pandas.Series.tz_convert.html

Documentation problem

The documentation for this function lacks examples and returns {klass} instead of "Series or DataFrame"

Suggested fix for documentation

Add examples for this function and fix the Returns section

[mroeschke]

Looks like the {klass} parameterization wasn't filled in correctly. A PR to fix would be welcome!