docs: add docs about how to use CommandRunner

lib/command_runner.ex

@@ -15,6 +15,30 @@ defmodule CommandRunner do
             {CommandRunner, name: MyApp.CommandRunner}
           ]
 
+          Supervisor.start_link(
+            children,
+            strategy: :one_for_one,
+            name: MyApp.Supervisor
+          )
+        end
+      end
+
+  Alternatively, you can define your own command runner.
+
+      defmodule MyApp.CommandRunner do
+        use CommandRunner
+      end
+
+  You can also mount that in your supervision tree.
+
+      defmodule MyApp.Application do
+        use Application
+
+        def start(_type, _args) do
+          children = [
+            MyApp.CommandRunner
+          ]
+
           Supervisor.start_link(
             children,
             strategy: :one_for_one,