Add MQTT monitor with Home Assistant autodiscovery

Poll lifepo4wered-cli every 30s (configurable), publish all registers as
one JSON state payload, and announce sensors/binary sensor via MQTT
discovery. run.sh pulls broker credentials from the Supervisor mqtt
service (Mosquitto addon) with manual overrides in addon options.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -1,5 +1,37 @@
 # hassio-addon-lifepo4wered
 
+Home Assistant OS addon for the [LiFePO4wered/Pi+](https://lifepo4wered.com/lifepo4wered-pi+.html)
+UPS: runs `lifepo4wered-daemon` and publishes UPS stats to MQTT with Home
+Assistant autodiscovery.
+
+## MQTT monitor
+
+`lifepo4wered_monitor.py` polls `lifepo4wered-cli get` (default every 30 s)
+and publishes all registers as one JSON payload to `lifepo4wered/state`.
+Entities appear automatically under one device, "LiFePO4wered/Pi+":
+
+- **Sensors**: input/battery/output voltage (V), output current (A)
+- **Binary sensor** "External power": ON when `VIN >= VIN_THRESHOLD`
+  (i.e. OFF means running on battery)
+- **Diagnostics**: thresholds, timers, watchdog and state registers
+- **Availability**: `lifepo4wered/availability` with MQTT Last Will, so
+  entities go *unavailable* if the addon stops
+
+MQTT connection details are taken automatically from the Supervisor when the
+Mosquitto addon is installed. Addon options: `poll_interval` (seconds) and
+optional `mqtt_host`/`mqtt_port`/`mqtt_user`/`mqtt_password` overrides.
+
+### Testing off the Pi
+
+```
+python3 -m unittest discover -s tests            # unit tests, no deps needed
+LIFEPO4WERED_FAKE=1 MQTT_HOST=... python3 hassio-addon-lifepo4wered/lifepo4wered_monitor.py
+```
+
+`LIFEPO4WERED_FAKE=1` replaces the CLI with embedded sample data.
+
+## Setup notes
+
 
 https://www.linkedin.com/pulse/creating-your-first-home-assistant-add-on-issac-goldstand