Objects don't have a description via `kubectl explain`

[sebgoa]

Describe the bug
No description when running kubectl explain

$ kubectl explain brokers
KIND:     Broker
VERSION:  eventing.knative.dev/v1beta1

DESCRIPTION:
     <empty>
$ kubectl explain sinkbinding
KIND:     SinkBinding
VERSION:  sources.knative.dev/v1alpha2

DESCRIPTION:
     <empty>

Expected behavior
I expected a description like all other k8s objects.

Maybe it comes from the kubectl code and we cannot get explain to work on CRDs.

[lionelvillard]

related to #2609

[grantr]

Fixing #2609 (adding OpenAPI to CRDs) will fix this one.

[vaikas]

I started looking at this and thought about just fixing the "top level" description for the crd, and then I ran into this. Just jotting this down, not saying this is the problem, but...
kubernetes/kubernetes#82407

[nlopezgi]

/assign

I'm going to take a stab at helping with this one