docs: add docs for kkFileView preview (#82)

* Update preview.md

添加kkFileView配置示例与常见问题解决办法

* Update preview.md

tips of deploying and using kkFileView

* Update preview.md

Author: fanfan142

docs/config/preview.md

@@ -107,8 +107,25 @@ Deploying and using `OnlyOffice` Reference:
 - https://github.com/AlistGo/alist/discussions/3255
 - https://github.com/AlistGo/alist/discussions/8271
 
+:::tip
+If you want to use self-deployed kkFileView to preview more file formats,You can add the following configuration here:
+
+```json
+{
+  "doc,docx,xls,xlsx,xlsm,ppt,pptx,csv,tsv,dotm,xlt,xltm,dot,dotx,xlam,xla,pages": 
+  { 
+    "kkFileView": "https://kk.domain.com:8012/onlinePreview?url=$eb_url"
+  }
+}
+```
+
+Potential issues when deploying and using kkFileView:
+
+- Browser security policies prohibit mixed protocol usage. kkFileView uses HTTP by default. When accessing openlist via HTTPS, the browser may not support transmission. You can set base.url to HTTPS by adding environment variables, or modify base.url to HTTPS in /opt/kkFileView-4.x.0/config/application.properties of kkFileView.
+- When openlist embedded in an iframe communicates with lower-version kkFileView, cross-origin issues may occur due to different domain names. This can be resolved by configuring the Access-Control-Allow-Origin header in reverse proxy.
 :::
 
+
 ### **Audio cover**
 
 The default audio cover.

docs/zh/config/preview.md

@@ -108,6 +108,25 @@ interface {
 - https://github.com/AlistGo/alist/discussions/3255
 - https://github.com/AlistGo/alist/discussions/8271
 
+
+:::tip
+如果你想使用自部署的kkFileView预览更多格式文件，可以在这里添加如下配置：
+```json
+{
+  "doc,docx,xls,xlsx,xlsm,ppt,pptx,csv,tsv,dotm,xlt,xltm,dot,dotx,xlam,xla,pages": 
+  { 
+    "kkFileView": "https://kk.domain.com:8012/onlinePreview?url=$eb_url"
+  }
+}
+```
+部署和使用 `kkFileView` 可能存在以下问题：
+
+- 浏览器安全策略禁止混合使用协议，kkFileView默认使用http进行传输，当使用https访问openlist时，浏览器不支持传输，
+  可通过添加环境变量设置base.url为https
+  或修改kkFileView中的/opt/kkFileView-4.x.0/config/application.properties中的base.url为https
+
+- 嵌入iframe的openlist与低版本kkFileView传输时域名不同存在跨域问题，可通过反向代理配置Access-Control-Allow-Origin请求头解决
+
 :::
 
 ## **音频封面**