mod:add dropbox to drop online api (#73)

Author: SenkjM

docs/.vuepress/public/img/drivers/dropbox/7.png

@@ -24,8 +24,10 @@ Dropbox Official：https://www.dropbox.com/
 
 
 ## **Get refresh token**
-
-- The steps are as follows:
+- **This cloud drive does not support the online API mode provided by OpenList.**  
+  - The following tutorial applies when the option is kept disabled as shown below.  
+  ![Disable online_api](/img/drivers/dropbox/7.png)
+  - The steps are as follows:
   - If you create your own `Client ID` and `Secret`, remember to authorize them.
   - First, [click here](https://www.dropbox.com/developers/apps?_tk=pilot_lp&_ad=topbar4&_camp=myapps) to enter the Dropbox app management page and click "Create App".
   ![Enter the page](/img/drivers/dropbox/1.png)

docs/guide/drivers/dropbox.md

@@ -24,6 +24,9 @@ Dropbox官网：https://www.dropbox.com/
 
 
 ## **获取刷新令牌**
+- **该网盘并不支持由OpenList提供的online api模式**
+  以下教程适用于保持如框内所示的关闭状态
+  ![关闭online_api](/img/drivers/dropbox/7.png)
   - 获取方式如下
   - 自建`客户端ID`和`秘钥`时，记得授权
   - 首先[点击这里](https://www.dropbox.com/developers/apps?_tk=pilot_lp&_ad=topbar4&_camp=myapps)进入dropbox的应用管理界面，点击创建应用