docs(CONTRIBUTION): Add missing link for `Accquire the submitted file…

…s` (#3102)

Ref atian25's suggestions at: #3066.

docs/source/en/basics/controller.md

@@ -312,7 +312,7 @@ If user request exceeds the maximum length for parsing that we configured, the f
 
 ### Acquire the submitted files
 
-The `body` in the request can carry parameters as well as files. Generally speaking, our browsers always send files in `multipart/form-data`, and we now have two kinds of ways supporting submitting and acquiring files with the help of Egg's Multipart as a plug-in.
+The `body` in the request can carry parameters as well as files. Generally speaking, our browsers always send files in `multipart/form-data`, and we now have two kinds of ways supporting submitting and acquiring files with the help of the framework's plug-in [Multipart](https://github.com/eggjs/egg-multipart).
 
 - #### `File` Mode:
 If you have no ideas about Nodejs's Stream at all, the `File` mode suits you well:

docs/source/zh-cn/basics/controller.md

@@ -314,7 +314,7 @@ module.exports = {
 
 ### 获取上传的文件
 
-请求 body 除了可以带参数之外，还可以发送文件。一般来说，浏览器上都是通过 `multipart/form-data` 格式发送文件的，在 Egg 的 Multipart 插件中，我们为你提供了两种方式上传和接受文件：
+请求 body 除了可以带参数之外，还可以发送文件，一般来说，浏览器上都是通过 `Multipart/form-data` 格式发送文件的，框架通过内置 [Multipart](https://github.com/eggjs/egg-multipart) 插件来支持获取用户上传的文件，我们为你提供了两种方式：
 
 - #### File 模式：
 如果你完全不知道 Nodejs 中的 Stream 用法，那么 File 模式非常合适你：