examples, oneshot services rework

Signed-off-by: fbt <fbt@fleshless.org>

examples/services/iptables

@@ -0,0 +1,11 @@
+#!/usr/bin/env ssm
+
+service_oneshot = true
+service_command = /usr/bin/false
+
+service::pre_start() {
+	cat <<- EOF
+		Please don't. Use ferm or any other wrapper.
+		You will just reinvent one in here anyway.
+	EOF
+}