specs: Update spark spec docs to reference `quilt logs`
specs: Update spark spec docs to reference `quilt logs`

Preceding commits in this PR add a `quilt logs` command, which should
be suggested over `swarm logs` (alike `swarm ps` -> `quilt containers`).

kelda/kelda,mmussomele/quilt,stevenlin598/quilt,PenguinToast/quilt,NetSys/quilt,quilt/quilt,kklin/quilt,NetSys/quilt,quilt/quilt,ejj/quilt-dev,mmussomele/quilt,kklin/kelda,kayousterhout/quilt,LuiseV/quilt,tejasmanohar/quilt,ejj/quilt-dev,stevenlin598/quilt,stevenlin598/quilt,kklin/kelda,kelda/kelda,NetSys/quilt,stevenlin598/quilt,tejasmanohar/quilt,kklin/kelda,mmussomele/quilt,kelda/kelda,stevenlin598/quilt,quilt/quilt,PenguinToast/quilt,NetSys/quilt,kklin/quilt,LuiseV/quilt,ejj/quilt-dev,stevenlin598/quilt,NetSys/quilt,ejj/quilt-dev,quilt/quilt,PenguinToast/quilt,kelda/kelda,tejasmanohar/quilt,mmussomele/quilt,kklin/quilt,kayousterhout/quilt,kayousterhout/quilt,tejasmanohar/quilt,kklin/quilt,PenguinToast/quilt,mmussomele/quilt,LuiseV/quilt,kklin/kelda,PenguinToast/quilt,kayousterhout/quilt,LuiseV/quilt,mmussomele/quilt,LuiseV/quilt