Weka page for RapidMiner extension

[DraXus]

Add a roadmap and further documentation to RapidMiner extension wiki page: https://github.com/openml/OpenML/wiki/RapidMiner-extension

[joaquinvanschoren]

Agreed. There is absolutely no documentation right now?

[joaquinvanschoren]

This issue was moved to openml/openml-java#14