Kind: document kubernetes behavior with image side loading and :latest tag

[figo]

steps to reproduce:
1) build a container with tag: latest,
2) then load into kind, no error reported:
kind load docker-image ###:latest
3) then deploy pod to kind, check pod status, it getting image Pull Error.

it works well with other numeric tag as i tested.
thanks to @BenTheElder to point it out.

[BenTheElder]

This is a Kubernetes feature, and we should document it and how to work around:

https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.10/#container-v1-core

imagePullPolicy string | Image pull policy.
One of Always, Never, IfNotPresent. Defaults to Always if :latest tag is specified, or IfNotPresent otherwise. Cannot be updated. More info: 
https://kubernetes.io/docs/concepts/containers/images#updating-images

(emphasis mine on Defaults to Always if :latest tag is specified)

[BenTheElder]

/kind documentation
/priority important-soon

work arounds are:

• don't use a :latest tag
• specify imagePullPolicy: IfNotPresent or imagePullPolicy: Never on your container(s)

[BenTheElder]

@tao12345666333 documented this 🙏
https://kind.sigs.k8s.io/docs/user/quick-start/#loading-an-image-into-your-cluster