Add missing line for authelia authentication

Lines for authelia authentication seems to be missing in the server part of the openhab conf file.
This PR are the missing line.

openhab.subdomain.conf.sample

@@ -14,6 +14,9 @@ server {
     # enable for ldap auth, fill in ldap details in ldap.conf
     #include /config/nginx/ldap.conf;
 
+    # enable for Authelia
+    #include /config/nginx/authelia-server.conf;
+
     location / {
         # enable the next two lines for http auth
         #auth_basic "Restricted";