message: docs: add more description at `Authentication`
diff: @@ -43,21 +43,22 @@ client.record
  | Name | Type | Required | Description |
  | ------------------ | :--------------: | :-------------------------: | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
  | baseUrl | String | Conditionally<br />Required | The base URL for your Kintone environment.<br />It must start with `https`. (e.g. https://example.kintone.com) <br />Required in Node.js environment. If you omit it in browser environment, `location.origin` will be used. |
  -| auth | Object | Conditionally<br />Required | |
  -| guestSpaceId | Number or String | | The guest space ID. If you operate apps made inside a guest space, please specify this. |
  -| basicAuth | Object | | If your Kintone environment uses [Basic authentication](https://developer.kintone.io/hc/en-us/articles/212495188#basicauthentication), please specify its username and password. |
  +| auth | Object | Conditionally<br />Required | The object for authentication. See [Authentication](#Authentication). |
  +| guestSpaceId | Number or String | | The guest space ID. If you are dealing with apps that are in guest spaces, please specify this. |
  +| basicAuth | Object | | If your Kintone environment uses Basic authentication, please specify its username and password. |
  | basicAuth.username | String | | The username of Basic authentication. |
  | basicAuth.password | String | | The password of Basic authentication. |
  ### Authentication
  -This client supports three authentication methods:
  +The client supports three authentication methods:
  1. [Password authentication](https://developer.kintone.io/hc/en-us/articles/212495188#passwordAuth)
  2. [API token authentication](https://developer.kintone.io/hc/en-us/articles/212495188#APItokenAuth)
  3. [Session authentication](https://developer.kintone.io/hc/en-us/articles/212495188#sessionAuth)
  -> _TODO: Something like: "The required parameters are different by the methods. The client judges which method to use by passed parameters"_
  +The required parameters inside `auth` are different by the methods.
  +The client determines which method to use by passed parameters.
  #### 1. Parameters for [Password authentication](https://developer.kintone.io/hc/en-us/articles/212495188#passwordAuth)
  