message: docs: add documentation for app.getAppSettings
diff: - [getAppCustomize](#getAppCustomize)
  - [updateAppCustomize](#updateAppCustomize)
  +- [getAppSettings](#getAppSettings)
  ## Overview
  @@ -94,3 +95,38 @@ A `CustomizationFileForUpdate` object has the following properties:
  #### Reference
  - https://developer.kintone.io/hc/en-us/articles/115004873968
  +
  +### getAppSettings
  +
  +Gets the description, name, icon, revision and color theme of an App.
  +
  +#### Parameters
  +
  +| Name | Type | Required | Description |
  +| ------- | :--------------: | :------: | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
  +| app | Number or String | Yes | The App ID. |
  +| lang | String | | The localized language to retrieve the data in:<br />- `default`: retrieves the default names<br />- `en`: retrieves the localized English names<br />- `zh`: retrieves the localized Chinese names<br />- `ja`: retrieves the localized Japanese names<br />- `user`: retrieves the localized names, in the same language as the language setting\* set on the user used for the authentication.<br /><br />If ignored, the default names will be retrieved. |
  +| preview | Boolean | | A flag whether to get the customization settings for pre-live environment |
  +
  +\*If the user language setting is set to "Use Web browser settings", the settings set in the Accept-Language header will be used. If there is no Accept-Language header, the language set in the "Localization" settings in the System Administrator's menu will be used.
  +
  +#### Returns
  +
  +| Name | Type | Description |
  +| --------------------- | :----: | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
  +| name | String | The App name. |
  +| description | String | The App description in HTML format. |
  +| icon | Object | An object containing data of the App icon. |
  +| icon.file | Object | An object containing data of uploaded icon files. |
  +| icon.file.contentType | String | The MIME type of the uploaded icon file. |
  +| icon.file.fileKey | String | The fileKey of the uploaded icon file. |
  +| icon.file.name | String | The file name of the uploaded icon file. |
  +| icon.file.size | String | The byte size of the uploaded icon file. |
  +| icon.key | String | The key identifier of the icon.<br />Responded, if the preset icons within kintone are used. |
  +| icon.type | String | The icon type:<br />- `FILE`: An uploaded image.<br />- `PRESET`: A preset icon within kintone. |
  +| revision | String | The revision number of the App settings. |
  +| theme | String | The color theme. Possible values are: `WHITE`, `RED`, `BLUE`, `GREEN`, `YELLOW`, `BLACK`.<br />Apps created before February 2017 may respond with the following classic themes:`CLIPBOARD`, `BINDER`, `PENCIL`, `CLIPS`. |
  +
  +#### Reference
  +
  +- https://developer.kintone.io/hc/en-us/articles/115004811668
  