For supporting ovnkube-trace running on RHEL8 platform, should copy file from /usr/lib/rhel8/ovnkube-trace, so need to update doc with a note for this

4.14

always

1. copy file from /usr/lib/rhel8/ovnkube-trace to the local, local is a RHEL8 platform
$ cat /etc/redhat-release 
Red Hat Enterprise Linux release 8.6 (Ootpa)
$ POD=$(oc get pods -n openshift-ovn-kubernetes -l app=ovnkube-control-plane -o name | head -1 | awk -F '/' '{print $NF}')
$ oc cp -n openshift-ovn-kubernetes $POD:/usr/lib/rhel8/ovnkube-trace -c ovnkube-cluster-manager ovnkube-trace
tar: Removing leading `/' from member names
$ chmod +x ovnkube-trace

2.  running ovnkube-trace tools
$ ./ovnkube-trace -src-namespace test -src hello-pod -dst-namespace openshift-dns -dst dns-default-9dgxc -udp -dst-port 53
ovn-trace source pod to destination pod indicates success from hello-pod to dns-default-9dgxc
ovn-trace (remote) source pod to destination pod indicates success from hello-pod to dns-default-9dgxc
ovn-trace destination pod to source pod indicates success from dns-default-9dgxc to hello-pod
ovn-trace (remote) destination pod to source pod indicates success from dns-default-9dgxc to hello-pod
ovs-appctl ofproto/trace source pod to destination pod indicates success from hello-pod to dns-default-9dgxc
ovs-appctl ofproto/trace destination pod to source pod indicates success from dns-default-9dgxc to hello-pod
ovn-detrace source pod to destination pod indicates success from hello-pod to dns-default-9dgxc
ovn-detrace destination pod to source pod indicates success from dns-default-9dgxc to hello-pod