Add OpenRC service and basic documentation

README.md

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+# unifi-shutd
+This is a simple daemon that monitors the in-built NUT server on a Ubiquiti UniFi UPS and safely shuts down the active system when the UPS switches to battery power (on AC loss).
+
+## Usage
+1. Install the `unifi-shutd` daemon to `/usr/local/bin/unifi-shutd`.
+2. Install the service file for your init system (be sure to edit the arguments first!!)
+    - OpenRC: Save [services/openrc](https://raw.githubusercontent.com/rwinkhart/unifi-shutd/refs/heads/main/services/openrc)` to `/etc/init.d/unifi-shutd`
+    - systemd: Not yet implemented (feel free to contribute; I just haven't bothered because all my baremetal servers are based on Alpine Linux)
+3. Enable and start the service
+4. Test disconnecting your UPS from AC and ensure the service properly shuts down your server

services/openrc

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+#!/sbin/openrc-run
+supervisor=supervise-daemon
+
+name="UniFi UPS safe shutdown"
+
+command="/usr/local/bin/unifi-shutd"
+command_args="<ip:port> <ups id> <scan interval> <bad scan limit>"
+
+depend() {
+        need net localmount
+        after firewall
+}