Adds am_lighthouse warning msg (#43)

* add warning message when am_lighthouse is enabled; update config templating

examples/quickstart-vagrant/ansible/roles/nebula/templates/config.yml.j2

@@ -42,8 +42,10 @@ lighthouse:
   am_lighthouse: false
 {% endif %}
   interval: 60
+{% if 'generic' in group_names %}
   hosts:
     - {{ hostvars[groups['lighthouse'][0]][vagrant_ifce]['ipv4']['address'] | to_nebula_ip }}
+{% endif %}
   
 # Configure the private interface
 tun: