如何在API Blueprint中记录path中的可选参数？

## 路径 [/users/{id}{?fields}]

### 获取用户信息 [GET]

+ Parameters
    + id (string, required) - 用户ID
    + fields (string, optional) - 返回的字段，多个字段使用逗号分隔，默认为所有字段

+ Request (application/json)

    + Headers

            Authorization: Bearer {access_token}

+ Response 200 (application/json)

    + Body

            {
                "id": "123456",
                "name": "John Doe",
                "email": "john.doe@example.com"
            }