add demo project which uses the nuget package

[joslat]

add demo project which uses the nuget package
must be not in the main solution, but standalone
maybe in a folder named demos or examples

[joslat]

Work started in branch: https://github.com/fuwei007/OpenAI-realtimeapi-dotnetsdk/tree/joslat-add-demo
At the moment getting this together (quite advanced but not fully working).

[joslat]

Solved, PR here: #66