List KVM2 driver in README.md.
List KVM2 driver in README.md.

Update the minikube README to make it more clear that the
KVM driver is deprecated in favor of the KVM2 driver.
dims/minikube,aaron-prindle/minikube,kubernetes/minikube,dalehamel/minikube,warmchang/minikube,kubernetes/minikube,kubernetes/minikube,warmchang/minikube,dlorenc/minikube,r2d4/minikube,dlorenc/minikube,kubernetes/minikube,dlorenc/minikube,dalehamel/minikube,aaron-prindle/minikube,r2d4/minikube,dalehamel/minikube,warmchang/minikube,dlorenc/minikube,warmchang/minikube,aaron-prindle/minikube,dlorenc/minikube,warmchang/minikube,warmchang/minikube,dims/minikube,r2d4/minikube,dims/minikube,kubernetes/minikube,kubernetes/minikube,warmchang/minikube,kubernetes/minikube,dlorenc/minikube,dlorenc/minikube,dlorenc/minikube