DOC: expanding comparison with R section
might be worth expanding the [comparison with R section](http://pandas.pydata.org/pandas-docs/stable/comparison_with_r.html); maybe have a basics section?

with some of the verbs from [here](http://nbviewer.ipython.org/urls/gist.githubusercontent.com/TomAugspurger/6e052140eaa5fdb6e8c0/raw/811585624e843f3f80b9b6fe89e18119d7d2d73c/dplyr_pandas.ipynb)

@TomAugspurger 
