server: libxtreemfs for Java: Added note in Volume.addReplica() interface docu...

server: libxtreemfs for Java: Added note in Volume.addReplica() interface docu that read only replicas always require a replication strategy as replication flag.

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@3535 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534