Add a README with a record/replay example

go/fake-http/README.md

# fake-http
## Example: Record and replay kubernetes traffic
This needs a running Minikube instance, which can be started with
`minikube start`.
```
$ fake-http -proxy-url=https://$(minikube ip):8443 -proxy-client-cert ~/.minikube/client.crt -proxy-client-key ~/.minikube/client.key
2018/06/09 13:21:19 Listening on http://localhost:8080
2018/06/09 13:21:19 See http://localhost:8080/_help
...
# switch to another terminal
# set up "fake-minikube" context
$ kubectl set-cluster fake-minikube --server=http://localhost:8080
$ kubectl set-context fake-minikube --cluster=fake-minikube --user minikube
$ kubectl --context=fake-minikube get pods
NAME                         READY     STATUS    RESTARTS   AGE
hellogo-2387138299-p83qw     1/1       Running   2          266d
hellonode-1839943766-t2hsv   1/1       Running   2          266d
```
Now have a look at the requests kubectl made: <http://localhost:8080>.
Or, save the log and replay it later:
```
$ curl -H 'Accept: application/yaml' http://localhost:8080/_log > minikube.yaml
# replay later
$ fake-http minikube.yaml
```