Update dashboard.md (#95)

* Update dashboard.md

Update：更新Dashboard反代中关于探针文件上传的反代配置

* Update dashboard.md

Update：update dashboard about proxy in file use

docs/guide/dashboard.md

@@ -99,7 +99,7 @@ location / {
     proxy_set_header Host $http_host;
     proxy_set_header      Upgrade $http_upgrade;
 }
-location ~ ^/(ws|terminal/.+)$  {
+location ~ ^/(ws|terminal/.+|file/.+)$ {
     proxy_pass http://127.0.0.1:8008;
     proxy_http_version 1.1;
     proxy_set_header Upgrade $http_upgrade;
@@ -124,6 +124,10 @@ proxy /terminal/* http://ip:8008 {
     websocket
     header_upstream -Origin
 }
+proxy /file/* http://ip:8008 {
+    websocket
+    header_upstream -Origin
+}
 ```
 
 ## 在宝塔面板中配置 SSL