powerbread: add README with wiring and usage

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

Author: rosterloh

applications/powerbread/README.md

@@ -1,7 +1,35 @@
 # PowerBread
 
-Dual-channel breadboard power monitor, ported from
-[XIAO-powerbread](https://github.com/nicho810/XIAO-powerbread).
-Wiring and usage docs are completed alongside the implementation.
+Dual-channel breadboard power monitor on the Adafruit QT Py ESP32-C3, ported
+from [XIAO-powerbread](https://github.com/nicho810/XIAO-powerbread): an
+INA3221 measures voltage/current/power on two supply rails, a 0.96" ST7735
+LCD shows an LVGL UI (dashboard, line chart, statistics), and a resistor-ladder
+dial wheel navigates it. Measurements stream as CSV over USB serial on demand.
 
-Build: `uv run poe app powerbread`
+## Wiring
+
+| Function          | QT Py pin | GPIO   | Notes                          |
+|-------------------|-----------|--------|--------------------------------|
+| INA3221 SDA/SCL   | SDA/SCL   | 5 / 6  | Stemma QT, addr 0x40, 50 mR shunts |
+| LCD DIN (MOSI)    | MO        | 7      | SPI2                           |
+| LCD CLK           | SCK       | 10     | SPI2                           |
+| LCD DC            | MI        | 8      | re-pinmuxed from SPI2 MISO     |
+| LCD RST           | A3        | 0      |                                |
+| LCD CS            | —         | —      | tied low on the module         |
+| Dial wheel ladder | A2 / D2   | 1      | ADC1 channel 1                 |
+
+## Controls
+
+- Dial up/down: cycle mode (dashboard → chart → stats)
+- Dial short press: switch focused channel (1 ↔ 2)
+- Dial long press (≥1 s): reset stats and energy counters
+
+Shell (USB serial), root command `powerbread`:
+`read`, `reset`, `stream <on|off>` (CSV: `t_ms,ch,mV,mA,mW`),
+`mode <dash|chart|stats>`, `channel <1|2>`, `dial` (raw dial mV, for
+calibrating the `adc-keys` thresholds in the board overlay).
+
+## Build & flash
+
+    uv run poe app powerbread
+    uv run poe flash powerbread