(README) Added caution about openjdk and Cassandra
(README) Added caution about openjdk and Cassandra

simong/Hilary,mrvisser/Hilary,jfederico/Hilary,ExC0d3/Hilary,stuartf/Hilary,nicolaasmatthijs/Hilary,mrvisser/Hilary,Orodan/Hilary,ExC0d3/Hilary,timdegroote/Hilary,Orodan/Hilary,simong/Hilary,stuartf/Hilary,jfederico/Hilary,timdegroote/Hilary,nicolaasmatthijs/Hilary,Coenego/Hilary