[www] add link to Telemetry Event service (panko)
[www] add link to Telemetry Event service (panko)

Change-Id: I750e89fb3512ead66b34e9960fa8b5dd5bfcfa7f

openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals