Mention application/json and text/csv under 7.9.5 Serialization

All,

We mention the "serialization attribute value of "application/json"" in
section 3.2.2.2.

But under 7.9.5, we don't mention application/json or text/csv, while we
detail the other serializations. We should probably do so, if only as
a reference to 3.2.2.2. Same for text/csv.

-Erik