datatable - make it clearer that you can build custom sorting functions with python

[miketerp]

Based on dash-datatables (https://dash.plotly.com/datatable), a customer was interested about datatable's "custom" sorting feature. I understand that this example is available at https://dash.plotly.com/datatable/callbacks as "Python-Driven Filtering, Paging, Sorting". I'm wondering if we can re-word some parts of the docs or something to provide more visibility.