Docs: add type query parameter usage for preview (src AlistGo/alist-web#177) (#349)

Author: potoo0

docs/config/preview.md

@@ -115,3 +115,20 @@ Whether to automatically play video files.
 ### **Proxy ignore headers**
 
 For details, please check:  **https://github.com/alist-org/alist/issues/2763**
+
+### **Force preview**
+
+We can force the preview type through the `type` query parameter.
+
+Available values:
+
+```
+UNKNOWN
+FOLDER
+VIDEO
+AUDIO
+TEXT
+IMAGE
+```
+
+Example: `http://yourdomain/test-file.ahk?type=text`

docs/zh/config/preview.md

@@ -117,3 +117,19 @@ interface {
 
 详情查看： **https://github.com/alist-org/alist/issues/2763**
 
+### **强制预览**
+
+可以通过 `type` 请求参数来强制设置预览类型。
+
+可选值:
+
+```
+UNKNOWN
+FOLDER
+VIDEO
+AUDIO
+TEXT
+IMAGE
+```
+
+示例: `http://yourdomain/test-file.ahk?type=text`