runtime_thread_stats: mention the new Runtime Tuning guide in help

deps/rabbitmq_cli/lib/rabbitmq/cli/core/doc_guide.ex

@@ -64,6 +64,7 @@ defmodule RabbitMQ.CLI.Core.DocGuide do
   Macros.defguide("plugins")
   Macros.defguide("queues")
   Macros.defguide("quorum_queues", domain: "next.rabbitmq.com")
+  Macros.defguide("runtime_tuning", path_segment: "runtime")
   Macros.defguide("tls", path_segment: "ssl")
   Macros.defguide("troubleshooting")
   Macros.defguide("virtual_hosts", path_segments: "vhosts")

deps/rabbitmq_cli/lib/rabbitmq/cli/diagnostics/commands/runtime_thread_stats_command.ex

@@ -14,6 +14,8 @@
 ## Copyright (c) 2007-2019 Pivotal Software, Inc.  All rights reserved.
 
 defmodule RabbitMQ.CLI.Diagnostics.Commands.RuntimeThreadStatsCommand do
+  alias RabbitMQ.CLI.Core.DocGuide
+
   @behaviour RabbitMQ.CLI.CommandBehaviour
 
   def switches(), do: [sample_interval: :integer]
@@ -63,6 +65,12 @@ defmodule RabbitMQ.CLI.Diagnostics.Commands.RuntimeThreadStatsCommand do
     ]
   end
 
+  def usage_doc_guides() do
+    [
+      DocGuide.runtime_tuning()
+    ]
+  end
+
   def banner([], %{node: node_name, sample_interval: interval}) do
     "Will collect runtime thread stats on #{node_name} for #{interval} seconds..."
   end