Remove reference to k8s directory from README
Remove reference to k8s directory from README

Kolla has moved away from Kubernetes and is now using docker-compose to
define container sets.

Remove last reference to Kubernetes in the README file, and document
the `compose` directory instead.

Change-Id: Ic586da2ae7859817c0da888f6ce5c788188e43d2

HackToday/kolla,HackToday/kolla,negronjl/kolla,toby82/kolla,stackforge/kolla,stackforge/kolla,bdastur/kolla,fdumpling/kolla,invenfantasy/kolla,limamauricio/mykolla,meticulo3366/kolla,mrangana/kolla,rajalokan/kolla,coolsvap/kolla,dardelean/kolla-ansible,limamauricio/mykolla,coolsvap/kolla,intel-onp/kolla,openstack/kolla,jakedahn/kolla,mandre/kolla,fdumpling/kolla,mandre/kolla,brk3/kolla,dardelean/kolla-ansible,tonyli71/kolla,mandre/kolla,openstack/kolla,invenfantasy/kolla,LoHChina/kolla,mrangana/kolla,LoHChina/kolla,negronjl/kolla,GalenMa/kolla,HackToday/kolla,chenzhiwei/kolla,stackforge/kolla,fdumpling/kolla,invenfantasy/kolla,tonyli71/kolla,negronjl/kolla,jakedahn/kolla,brk3/kolla,intel-onp/kolla,GalenMa/kolla,LoHChina/kolla,nihilifer/kolla,jakedahn/kolla,rahulunair/kolla,rajalokan/kolla,coolsvap/kolla,rahulunair/kolla,limamauricio/mykolla,rajalokan/kolla,chenzhiwei/kolla,nihilifer/kolla,toby82/kolla,dardelean/kolla-ansible,chenzhiwei/kolla,meticulo3366/kolla,toby82/kolla,bdastur/kolla