QPID-5610 , QPID-5578 : Modify the QMF2 broker plugin README file to be correct with respect to type vs. pluginType

git-svn-id: https://svn.apache.org/repos/asf/qpid/branches/QPID-5610-maven3-build-qmf-tools@1591847 13f79535-47bb-0310-9956-ffa450edef68