README: include rtslib and SELINUX info
README: include rtslib and SELINUX info

Updated to explain the dependency on python-rtslib for interaction with the LIO metadata held in configfs. Also included information relating to running the pmda in SELINUX environments.
adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp