Use correct example for recurring.yml in ReadMe.md

[Joerg-Seitz]

When using the production:-key as suggested in the example from the README the recurring tasks are not properly loaded from recurring.yml because this level of the hash does not have a :schedule key.

See https://github.com/rails/solid_queue/blob/main/lib/solid_queue/configuration.rb#L174

without production: key

betterplace(dev):001> SolidQueue::Configuration.new.send(:recurring_tasks)
=>
[#<SolidQueue::RecurringTask:0x0000000136837f48
  id: nil,
  key: "tor_ips_updater",
  schedule: "0 */4 * * *",
  command: nil,
  class_name: "TorIpsUpdater",
  arguments: [],
  queue_name: nil,
  priority: nil,
  static: true,
  description: nil,
  created_at: nil,
  updated_at: nil>,
...

with production: key

betterplace(dev):003> SolidQueue::Configuration.new.send(:recurring_tasks)
=> []