Auto merge of #950 - wezm:update-freebsd-ci-image, r=alexcrichton

Update the FreeBSD CI image

As per #948 and #799 the FreeBSD CI qemu image needs to be updated to FreeBSD 11. I have done this and updated the README with the detailed steps taken. The new image is available for download at: http://bsd-ci.com/FreeBSD-11.1-RELEASE-amd64.qcow2.xz