Add IPv6 info to README.md
Add IPv6 info to README.md

Signed-off-by: Julien 'Lta' BALLET <1a73af9e7ae00182733b2292511b814be66f065f@lta.io>

chef-cookbooks/iptables,chef-cookbooks/iptables,opscode-cookbooks/iptables,opscode-cookbooks/iptables,opscode-cookbooks/iptables,chef-cookbooks/iptables