Add note to notifier_env in case someone else updates it someday.

playbooks/roles/notifier/templates/notifier_env.j2

 # {{ ansible_managed }}
 
+# Note this is used directly by the scheduler but not
+# by the workers.  Worker environment is set in supervisor
+# config.
 {% do notifier_env_vars.update(NOTIFIER_ENV_EXTRA) %}
 {% for name,value in notifier_env_vars.items() %}
 {% if value %}