support bi-directional mavlink

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

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

@@ -42,9 +42,11 @@ dfu-util --alt 0 --dfuse-address 0x08000000:leave \
 | `GND` | `G` |
 | `TX` | `R1` |
 
-The transmitter emits unsigned MAVLink 2 at 115200 baud, 8N1. It is binary
+The firmware emits unsigned MAVLink 2 at 115200 baud, 8N1. It is binary
 data, not terminal text. Read it with the python decoder:
 
 ```sh
-./scripts/read-mavlink.py $serial_device_path
+./scripts/test-mavlink.py $serial_device_path
 ```
+
+The test helper sends MAVLink `TIMESYNC` and`PING` frames while printing all received MAVLink messages.