Add pin header and connector description document (pin.md)

Signed-off-by: YoungSoo Shin <shinys000114@gmail.com>

docs/pin.md

@@ -0,0 +1,49 @@
+# Connector and Pin Header Description
+
+## J1 USB-C Connector
+
+This terminal is for uploading firmware and checking program logs.
+It is recognized as a serial device and as a `ttyACM` device in Linux.
+To view the logs, you can use the command below.
+
+```bash
+minicom -D /dev/ttyACM0 -b 115200
+```
+
+## J2 UART Pin header
+
+Connected to the `U0RXD`, `U0TXD` system UART of the ESP32-C3. Currently not used on this board.
+
+## J3 ODROID UART Connector
+
+Connects to the UART debug port of the ODROID.
+You can use the [cable from the USB-UART 2 board](https://www.hardkernel.com/shop/usb-uart-2-module-kit-copy/).
+
+## J4 GPIO Output
+
+4 GPIO output pin headers. Used to trigger the power of external devices.
+
+| Pin Number | Function           | Function           | Pin Number |
+|------------|--------------------|--------------------|------------|
+| 3          | Reserved           | Reserved           | 1          |
+| 4          | Reset (Open Drain) | Power (Open Drain) | 2          |
+
+The Reset and Power pins can be used on the ODROID-M series and H series.
+
+## J5 DC Input
+
+Supports 9~21v input. You can use the DC power supply sold by Hardkernel.
+
+## J6 DC Out
+
+Outputs the switched power from the J5 input.
+
+## J7 USB Power Out
+
+Switched 5v voltage output.
+
+## J8 OLED Display Connector
+
+**Reserved**
+
+SSD1309 OLED Connector