Add link to Debian Jessie box in README file.
Add link to Debian Jessie box in README file.

DavBfr/vagrant-lxc-base-boxes,Val/vagrant-lxc-base-boxes,sephii/vagrant-lxc-base-boxes,DavBfr/vagrant-lxc-base-boxes,fgrehm/vagrant-lxc-base-boxes,obnoxxx/vagrant-lxc-base-boxes