for each JSON service, the documentation of the service should note that inputs should be "json-able" julia objects, not raw json

[ericphanson]

xref #673 (comment)

For DynamoDB, the docs start with

This page documents function available when using the Dynamodb module, created with [@service Dynamodb](https://juliacloud.github.io/AWS.jl/stable/aws.html#AWS.@service-Tuple{Symbol,%20Vararg{Any}}).

I think it should say:

This page documents function available when using the Dynamodb module, created with [@service Dynamodb](https://juliacloud.github.io/AWS.jl/stable/aws.html#AWS.@service-Tuple{Symbol,%20Vararg{Any}}).

## Inputs

All inputs to Dynamodb functions should be passed as Julia objects, such as nested `Dict`s, rather than raw JSON.

## Table of contents

Ideally it would have an example also, but those we would have to manually write per-service, whereas this sentence we could autogenerate and stick in for all JSON services. (Or all services? not sure)