3.10 Input Objects - clarify lists are permitted as Input fields

[msolomon]

A minor omission in 3.10 Input Objects confused me briefly today by suggesting lists might not be permitted as the type of an input field. However, they are (and are even used in the examples), so add it in.

Alternatively, the kinds of permitted fields could be described explicitly as they are under Field Arguments: https://spec.graphql.org/draft/#sel-GAHZjCZABABDukZ

I believe this is simply an editing mistake.