Docs: table for `model.toml` params too narrow

[alexdewar]

The table for the model.toml params is too narrow (see screenshot below) and you end up having to scroll sideways to read it, which is annoying.

I think the proximate reason for this is that we have some very long param names (e.g. remaining_demand_absolute_tolerance) which are not wrappable and cause the first column to be very wide.

This wouldn't be such a problem if the total width of the page given over to text were larger. I'm not sure what the cleanest way to do with mdbook is, but you can add custom theming. There might be a simpler way, though.

[tsmbland]

I think we should reduce the font size in tables as well