Document how to start zenoh router in launch file

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Thank you! IMO, this explanation should be documented in the launch file. Otherwise 👍 from me
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_Originally posted by @henningkayser in https://github.com/CihatAltiparmak/moveit_middleware_benchmark/pull/22#issuecomment-2284065749_

Note: rmw_zenoh is still in development and there is a PR to remove tty stuffs. It can be good to wait a little bit.