Add notes about CSP

Signed-off-by: Tommy <contact@tommytran.io>

README.md

@@ -21,3 +21,11 @@ Matrix Synapse Docker-Compose
 9. Uncomment the security options for postgres. Run `docker-compose up -d` again.
 10. Create a user for mjolnir
 11. Copy the config from https://github.com/matrix-org/mjolnir/blob/main/config/default.yaml to `./mjolnir/config/production.yaml` and edit it accordingly. If you want Mjolnir to recieve reports instead of Synapse, make it listen on `0.0.0.0:8081`. You will also need to uncomment the approprieate lines in `./swag/nginx/proxy-confs/synapse.subdomain.conf` as well.
+
+## Notes
+
+The CSP policies in `swag/nginx/ssl.conf` is slightly stricter on [ArcticFoxes Element](https://element.arcticfoxes.net) as it does not support third party servers:
+
+```
+add_header Content-Security-Policy "default-src 'none'; connect-src 'self' https://arcticfoxes.net https://matrix.arcticfoxes.net; font-src 'self'; img-src 'self' https://arcticfoxes.net https://matrix.arcticfoxes.net blob: data:; manifest-src 'self'; media-src https://matrix.arcticfoxes.net; script-src 'self' 'unsafe-eval' https://www.recaptcha.net https://www.gstatic.com; style-src 'self' 'unsafe-inline'; frame-src 'self' https://www.recaptcha.net blob:; frame-ancestors 'self'; block-all-mixed-content; base-uri 'none'";
+```

docker-compose.yml

@@ -99,6 +99,7 @@ services:
     ports:
       - 443:443
       - 80:80
+      - 8448:8448
     networks:
       - matrix
       - element