ref: dvc queue examples

[dberenbaum]

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Per https://github.com/iterative/dvc.org/pull/3715#issuecomment-1175471624, we should add some more examples in dvc queue ref.

• [ ] queue kill: kill multiple tasks
• [ ] queue start: start with multiple jobs
• [ ] queue start: add new task to started queue
• [ ] queue start: increase jobs on started queue
• [ ] queue stop: behavior with running tasks
• [ ] queue stop: --kill behavior
• [ ] queue remove: use --success --failed to remove all completed tasks