Add release notes for v3.1.1
Add release notes for v3.1.1

jeffbryner/MozDef,mpurzynski/MozDef,mpurzynski/MozDef,mozilla/MozDef,jeffbryner/MozDef,mpurzynski/MozDef,mozilla/MozDef,mozilla/MozDef,jeffbryner/MozDef,jeffbryner/MozDef,mozilla/MozDef,mpurzynski/MozDef