Add compatibility section to README
Add compatibility section to README

This commit adds a compatibility section to the README explaining our
Mesos compatibility guarantees.

denen99/mesos-dns,denen99/mesos-dns,vivint-smarthome/mesos-dns,alberts/mesos-dns,mcoffin/mesos-dns,vivint-smarthome/mesos-dns,mesosphere/mesos-dns,mesosphere/mesos-dns,saagie/mesos-dns,alberts/mesos-dns,mcoffin/mesos-dns