added permissions instruction to docker custom CA docs (#2710)

Co-authored-by: कारतोफ्फेलस्क्रिप्ट™ <netroy@users.noreply.github.com>

docs/hosting/configuration/configuration-examples/custom-certificate-authority.md

@@ -43,3 +43,9 @@ services:
             - 5678:5678
         image: docker.n8n.io/n8nio/n8n
 ```
+
+You should also give the right permissions to the imported certs. You can do this once the container is running (assuming n8n as the container name):
+
+```bash
+docker exec --user 0 n8n chown -R 1000:1000 /opt/custom-certificates
+```