Add examples

[thomas-fossati]

Linda Dunbar's review

"The document provides basic diagrams to illustrate the modes but lacks comprehensive examples of the header parameters in action. It would be nicer to add complete example encodings of COSE messages with the proposed parameter."

[thomas-fossati]

The only problem is that a realistic example can only be crafted once the codepoints are allocated.

Could pick two from "private use" for now and refresh when IANA gives us the real ones.