Added docstring to Columns.groupby
Added docstring to Columns.groupby

mjabri/holoviews,basnijholt/holoviews,vascotenner/holoviews,mjabri/holoviews,basnijholt/holoviews,mjabri/holoviews,ioam/holoviews,ioam/holoviews,vascotenner/holoviews,ioam/holoviews,vascotenner/holoviews,basnijholt/holoviews