Concurrency documentation

[medihack]

Hello!

The documentation is quite unclear about the difference between

run_queue:
  max_concurrent_runs: 15

and this one

run_coordinator:
  module: dagster.core.run_coordinator
  class: QueuedRunCoordinator
  config:
    max_concurrent_runs: 15

Does it do the same thing? Do I have to specify both?

The concurrency documentation also does not state whether the QueuedRunCoordinator is still necessary for concurrency when only using the max_concurrent_runs of run_queue (I guess so, as the DefaultRunCoordinator is not capable of running assets in parallel).