CONTRIBUTING: point developers to kubevirt-dev slack
CONTRIBUTING: point developers to kubevirt-dev slack

With great sorrow, we have to admit that our IRC channel is mostly dead.
Would-be contributors should be directed to where people hang out these
days, which is the Kubernetes slack and our #kubevirt-dev channel.

Signed-off-by: Dan Kenigsberg <184831158ae7531bcabc22617ed51e8717c81e93@redhat.com>

kubevirt/kubevirt,davidvossel/kubevirt,stu-gott/kubevirt,davidvossel/kubevirt,kubevirt/kubevirt,davidvossel/kubevirt,stu-gott/kubevirt,davidvossel/kubevirt,kubevirt/kubevirt,kubevirt/kubevirt,stu-gott/kubevirt,stu-gott/kubevirt