https://github.com/tldr-pages/tldr/pull/4494 added `kubectl describe` help, but the main page still doesn't mention it. Add a note about its usage.
This is an important command, but it exceeds the suggested limit of 8 examples (do subcommands count as "examples"?). We could instead replace the `kubectl get` example with `kubectl {{get|describe}}`, but I'm really not a fan of that, since they're two different subcommands.