Update docs: add uart.md

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

docs/uart.md

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+# UART Terminal
+
+> **Warning**
+> Data drop may occur depending on the communication quality.
+
+![uart.png](img/uart.png)
+
+You can see the UART terminal in the Device tab.
+
+You can specify the baud rate in `Setting > Device`, and the supported baud rates are 9600-1500000.
+
+![device.png](img/device.png)
+
+## ANSI Color
+
+Supports the color table of the terminal.
+
+```bash
+odroid@server:~$ TERM=xterm-256color /bin/bash
+```
+
+![color.png](img/color.png)
+
+![htop.png](img/htop.png)