Make note of knative-eventing being optional in README  (#1826)
Make note of knative-eventing being optional in README  (#1826)

Only Knative Serving is required for KFServing to work.
Knative Eventing is used for specific logger/metrics tracking
use cases, so a note is made in the README about eventing
being optional.
kubeflow/manifests,kubeflow/manifests