Add manual edit warning

Added text block from dns config file to warn user that manual changes to lighttpd config will be overwritten.
Slight cosmetic adjustments (tabs -> spaces).

advanced/lighttpd.conf.debian

@@ -9,6 +9,14 @@
 # the Free Software Foundation, either version 2 of the License, or
 # (at your option) any later version.
 
+###############################################################################
+#     FILE AUTOMATICALLY OVERWRITTEN BY PI-HOLE INSTALL/UPDATE PROCEDURE.     #
+# ANY CHANGES MADE TO THIS FILE AFTER INSTALL WILL BE LOST ON THE NEXT UPDATE #
+#                                                                             #
+#              CHANGES SHOULD BE MADE IN A SEPERATE CONFIG FILE:              #
+#                         /etc/lighttpd/external.conf                         #
+###############################################################################
+
 server.modules = (
 	"mod_access",
 	"mod_accesslog",