Add an example showing when parameters contain a variant

[ciozi137]

A cluster containing a variant will flatten to JSON but will not unflatten as one expects. See discussion here: https://lavag.org/topic/20236-cr-jsontext/page/7/#findComment-136680

[ciozi137]

The issue:

[ciozi137]

This would be preferred but puts more responsibility on the user of the JSON-RPC library. I'm not sure that the library itself can handle such cases automatically: