add missing docs for kubectl-kruise describe command

[furykerry]

kubectl-kruise describe command provide deep inspection of the kruise rollout objects, however its usage is undocumented. we can add an introduction page for kubectl-kruise in the rollout for related command: e.g. describe, approve and undo, and link to the kubectl-kruise docs.

The introduction page can refer to the one in argo rollout . One can put the page the user manual section of rollout document

[abhayguptas]

Hi, @furykerry! I would like to document the usage of the kubectl-kruise command and raise a PR to resovle this Issue. May I?

[furykerry]

sorry for the late apply, if you're still interested, i can assign you with the issue

[GautamBytes]

@furykerry , but this issue is already fixed by this pr , you can close this issue.