Auto height semantics for DataTable are not immediately obvious

[davetapley]

Just spent ten minutes writing up issue for DataTable not supporting newlines in cells before realizing it is supported but:

1. Must explicitly pass height=None to add_row (because default is 1), and:
2. add_rows doesn't accept height (and I've only ever used add_rows so didn't know about height 😞 ).

Would PR be welcome to caution this in the docs, and add height to add_rows? 🙏🏻