Add doc for Run istio agent in local machine

Contributors Docs
1

i have a local kube cluster, i can run istio discovery server in local machine, it’s easy, just run with kubeconf.

but i want run istio agent in local machine ( with compiled envoy), too many arguments, i don’t konw how to fill it.

2

https://events.istio.io/istiocon-2021/slides/c9t1-LocalIstioDevelopment-JohnHoward.pdf may help