add a reminder about port 80 (#1147)

Author: enoch85

lets-encrypt/activate-ssl.sh

@@ -209,6 +209,9 @@ then
         fi
         # Activate new config
         check_command bash "$SCRIPTS/test-new-config.sh" "$TLSDOMAIN.conf"
+msg_box "Please remember to keep port 80 (and 443) open so that Let's Encrypt can do the automatic renewal of the cert. If port 80 is closed the cert will expire in 3 months.
+
+You don't need to worry about security as port 80 is directly forwarded to 443, so no traffic will actually be on port 80, except for the forwarding to 443 (HTTPS)."
         exit 0
     fi
 else