The footer is not available yet. It's in the mid-term plan (6 months - 1 year).
As a workaround, you can display column-related information in an additional time header row (use TimeHeaders collection to define it and BeforeTimeHeaderRender event to fill the data/HTML).
There is also an option to sponsor the feature to get a fixed delivery date. Please contact firstname.lastname@example.org if you'd like to go this way.