Update reverse-proxies.zh-cn.md (go-gitea#21484)

add proxy header to nginx config example
```
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
```
Signed-off-by: rock2dust <[email protected]>

Signed-off-by: rock2dust <[email protected]>
Co-authored-by: Lunny Xiao <[email protected]>

Author: rock2dust

docs/content/doc/usage/reverse-proxies.zh-cn.md

@@ -13,6 +13,12 @@ menu:
     identifier: "reverse-proxies"
 ---
 
+# 反向代理
+
+**目录**
+
+{{< toc >}}
+
 ## 使用 Nginx 作为反向代理服务
 
 如果您想使用 Nginx 作为 Gitea 的反向代理服务，您可以参照以下 `nginx.conf` 配置中 `server` 的 `http` 部分：
@@ -24,6 +30,10 @@ server {
 
     location / {
         proxy_pass http://localhost:3000;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
     }
 }
 ```
@@ -41,6 +51,10 @@ server {
     location /git/ { 
         # 注意: 反向代理后端 URL 的最后需要有一个路径符号
         proxy_pass http://localhost:3000/;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
     }
 }
 ```