Added a warning to the installation / setup script

See pull request #638 and issue #635 for more information.

setup/questions.sh

@@ -18,7 +18,8 @@ if [ -z "$NONINTERACTIVE" ]; then
 	message_box "Mail-in-a-Box Installation" \
 		"Hello and thanks for deploying a Mail-in-a-Box!
 		\n\nI'm going to ask you a few questions.
-		\n\nTo change your answers later, just run 'sudo mailinabox' from the command line."
+		\n\nTo change your answers later, just run 'sudo mailinabox' from the command line.
+		\n\nNOTE: You should only install this on a brand new Ubuntu installation 100% dedicated to Mail-in-a-Box. Mail-in-a-box will, for example, remove apache2."
 fi
 
 # The box needs a name.