boards/kakute-f7-mini-v3: add development docs

Signed-off-by: Onur Özkan <work@onurozkan.dev>

boards/kakute-f7-mini-v3/README.md

@@ -0,0 +1,49 @@
+# Kakute F7 Mini V3
+
+Kaptan support for the Holybro Kakute F7 Mini V3.
+
+The checked-in manufacturer manual is [Holybro_KakuteF7_Mini_V3_Manual_v1.0.pdf](Holybro_KakuteF7_Mini_V3_Manual_v1.0.pdf).
+
+## Build
+
+Build the firmware from the workspace root:
+
+```sh
+cargo build --release -p kaptan-kakute-f7-mini-v3 --features firmware --target thumbv7em-none-eabihf
+```
+
+Create its DFU (device firmware update) image:
+
+```sh
+./scripts/create-dfu-image.sh \
+  target/thumbv7em-none-eabihf/release/kaptan-kakute-f7-mini-v3 \
+  target/thumbv7em-none-eabihf/release/kaptan-kakute-f7-mini-v3.bin
+```
+
+The converter works with any firmware ELF. It uses rustup's `llvm-tools-preview` component which the workspace toolchain installs automatically.
+
+## Flash over USB DFU
+
+1. Disconnect the board from USB.
+2. Hold the `Boot` button.
+3. Connect USB, then release `Boot`. The board should enumerate as STM32 DFU.
+4. Flash the generated image:
+
+```sh
+dfu-util --alt 0 --dfuse-address 0x08000000:leave \
+  --download target/thumbv7em-none-eabihf/release/kaptan-kakute-f7-mini-v3.bin
+```
+
+## UART
+
+| USB-to-UART adapter | FC |
+| --- | --- |
+| `RX` | `T1` |
+| `GND` | `G` |
+| `TX` | `R1` |
+
+Open the serial device at 115200 baud, 8N1:
+
+```sh
+picocom --baud 115200 --databits 8 --parity n --stopbits 1 $serial_dev_path
+```