Add init.d script for OpenWrt.

Signed-off-by: Tom Wilkie <tom@grafana.com>

examples/openwrt-init.d/node_exporter

@@ -0,0 +1,13 @@
+#!/bin/sh /etc/rc.common
+
+START=99
+
+USE_PROCD=1
+PROG="/usr/bin/node_exporter"
+OPTIONS="--web.listen-address=:9100"
+
+start_service() {
+	procd_open_instance
+	procd_set_param command "$PROG" "${OPTIONS}"
+	procd_close_instance
+}