docs: clarify hc host default (#3385)
docs: clarify hc host default (#3385)

The default is actually the cluster name, not the ip

Signed-off-by: Snow Pettersen <snowp@squareup.com>

Mirrored from https://github.com/envoyproxy/envoy @ 2fa152da07db067cb0aedd1ef309759cb9424de6

lyft/envoy-api,lyft/envoy-api,lyft/envoy-api