message: docs: add nested topic example
diff: @@ -417,7 +417,8 @@ The help descriptions will be the description of the first command within a dire
  {
  "oclif": {
  "topics": {
  - "config": { "description": "manage heroku config variables" }
  + "apps:favorites": { "description": "manage favorite apps" },
  + "config": { "description": "manage heroku config variables" },
  }
  }
  }
  