add warning about security and the cluster private key
add warning about security and the cluster private key

lukemarsden/flocker,achanda/flocker,runcom/flocker,1d4Nf6/flocker,hackday-profilers/flocker,1d4Nf6/flocker,moypray/flocker,mbrukman/flocker,Azulinho/flocker,1d4Nf6/flocker,LaynePeng/flocker,w4ngyi/flocker,jml/flocker,runcom/flocker,achanda/flocker,AndyHuu/flocker,hackday-profilers/flocker,moypray/flocker,agonzalezro/flocker,mbrukman/flocker,LaynePeng/flocker,hackday-profilers/flocker,runcom/flocker,achanda/flocker,adamtheturtle/flocker,Azulinho/flocker,lukemarsden/flocker,wallnerryan/flocker-profiles,adamtheturtle/flocker,agonzalezro/flocker,Azulinho/flocker,wallnerryan/flocker-profiles,wallnerryan/flocker-profiles,agonzalezro/flocker,jml/flocker,mbrukman/flocker,adamtheturtle/flocker,lukemarsden/flocker,w4ngyi/flocker,LaynePeng/flocker,jml/flocker,AndyHuu/flocker,w4ngyi/flocker,moypray/flocker,AndyHuu/flocker