adding guide

done for [AGIOS-313](https://issues.jboss.org/browse/AGIOS-313)

@corinnekrych mind to review?
not yet unfortunately.. [we started a POC](https://github.com/cvasilak/aerogear-ios-cookbook/blob/1291b6f906af23274672157e84068f969dc70dfb/Buddies/Buddies/JsonSZResponseSerializer.swift) with @corinnekrych about it but with reached a block end with some generics issues we had and decided to leave it for next release until we comprehend it better.