DOC: Add comparison with Stata page to documentation
- [ ] closes #####
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

I noticed that the pandas documentation has pages for [Comparison with SAS](https://pandas.pydata.org/pandas-docs/stable/comparison_with_sas.html), [Comparison with R](https://pandas.pydata.org/pandas-docs/stable/comparison_with_r.html) and [Comparison with SQL](https://pandas.pydata.org/pandas-docs/stable/comparison_with_sql.html), but nothing for newcomers from Stata.

This is heavily based off of the "Comparison with SAS" page, with all the examples and discussion fixed for Stata.