Public Boxes with xenserver provider

[gokgozf]

https://atlas.hashicorp.com/boxes/search?provider=xenserver

I guess it might be good idea to include the available boxes to README.md
So the people who want to try finds an easy way to start

Best

[dertorsten]

From these boxes only one is accessible at all. All the boxes from Jonathan refer to xen-git.uk.xensource.com and this doesn't resolve in DNS as of 08/03/2017