README: clarify what CNI is
README: clarify what CNI is

The word "standard" does not represent what CNI is actually trying to
be.

kad/cni,achanda/cni,kad/cni,steveeJ/cni,murat1985/cni,squeed/plugins,appc/cni,containernetworking/cni,squeed/plugins,dcbw/cni,squaremo/cni,steveeJ/cni,luxas/cni,rosenhouse/cni,luxas/cni,containernetworking/cni,murat1985/cni,squaremo/cni,tomdee/cni,tangle329/cni,appc/cni,mcastelino/cni,dcbw/cni,containernetworking/plugins,rosenhouse/cni,containernetworking/plugins,tangle329/cni,achanda/cni,tomdee/cni,mcastelino/cni