converted to markdown and added edition clarification

FreeNAS-8.3.1-RELEASE-p2-x64.iso (Linux Compatiblity Client + linux-sun-jre1.7.0)
FreeNAS-8.3.1-RELEASE-p2-x64-jdk16.iso (FreeBSD Native + JDK16)
FreeNAS-8.3.1-RELEASE-p2-x64-openjdk7.iso (FreeBSD Native + OpenJDK7)