add note re. firewalld exclusion

Author: sjpb

roles/builder/defaults/main/dnf_packages.yml

@@ -74,4 +74,6 @@ dnf_specific_packages:
   # https://github.com/OSC/ood-ansible/blob/master/tasks/install-rpm.yml
   - ondemand
 
+  # NB: firewalld can't be installed in this image as it starts on boot, which is not wanted
+
 dnf_update_exclude: omit