Add Traefik information.

Using-a-Reverse-Proxy-with-Paperless-ngx.md

@@ -1,8 +1,10 @@
-[Nginx](#nginx) | [Apache](#apache) | [Caddy](#caddy)
+[Nginx](#nginx) | [Apache](#apache) | [Caddy](#caddy) | [Traefik](#traefik)
 
 If you want to expose paperless to the internet, you should hide it
 behind a reverse proxy with SSL enabled. The officially supported method is Nginx.
 
+If you get a `CSRF verification failed` error upon login, your compose or .env file is missing a valid [PAPERLESS_URL](https://docs.paperless-ngx.com/configuration/#PAPERLESS_URL) value.
+
 # Nginx
 
 In addition to the usual configuration for SSL, the following
@@ -157,4 +159,22 @@ Below is an example Caddy configuration
         header_down Referrer-Policy "strict-origin-when-cross-origin"
     }
 }
+```
+
+# Traefik
+
+Below is an example Traefik configuration you would add to the webserver container.
+- Make sure you replace `traefik_proxy` with the name of your own reverse proxy network.
+- Change the hostname to your own.
+- Adjust the entrypoints if needed. Usually `websecure`, some people have it setup as `https`.
+
+```
+    labels:
+      - "traefik.enable=true"
+      - "traefik.docker.network=traefik_proxy"
+      - "traefik.http.routers.paperless.rule=Host(`paperless.example.com`)"
+      - "traefik.http.routers.paperless.entrypoints=websecure"
+      - "traefik.http.routers.paperless.tls=true"
+      - "traefik.http.routers.paperless.tls.certresolver=letsencrypt"
+      - "traefik.http.services.paperless.loadbalancer.server.port=8000"
 ```