Update readme for broker certificates

Author: mrica-equinor

broker/README.md

@@ -97,3 +97,7 @@ Then attempt to publish something to the same topic in a different terminal
 ```
 mosquitto_pub -t topic_name -m hei -u admin -P secret_password --cafile ca-cert.pem
 ```
+
+## MQTT Broker Certificates
+
+If the CA and server certificates have expired, they should be generated by following the steps available on the [utility scripts](https://github.com/equinor/eq_robot_utility_scripts/blob/main/certificates/README.md) repository.