Documentation/applications/system: Add stty command documentation

Add documentation for the stty terminal configuration utility,
describing usage, available settings, examples, and configuration
options.

Signed-off-by: fangpeina <fangpeina@xiaomi.com>

Documentation/applications/system/stty/index.rst

@@ -0,0 +1,99 @@
+=================================
+``stty`` Terminal Configuration
+=================================
+
+Description
+-----------
+
+The ``stty`` command provides a standard Unix-like interface for viewing
+and configuring terminal (TTY) device settings at runtime via termios.
+It supports raw/cooked mode switching, individual flag control, baud
+rate configuration, and VMIN/VTIME parameters.
+
+Usage
+-----
+
+Basic Syntax
+^^^^^^^^^^^^
+
+.. code-block:: bash
+
+   stty [options] [settings...]
+
+Options:
+
+============== ==========================================================
+``-F <dev>``   Operate on the specified device instead of stdin
+``-h``         Show help message
+============== ==========================================================
+
+Settings
+^^^^^^^^
+
+=============  ==========================================
+Setting        Description
+=============  ==========================================
+``raw``        Set raw mode (no input/output processing)
+``cooked``     Set cooked mode (canonical with echo)
+``echo``       Enable echo
+``-echo``      Disable echo
+``icanon``     Enable canonical mode
+``-icanon``    Disable canonical mode
+``icrnl``      Map CR to NL on input
+``-icrnl``     Don't map CR to NL
+``onlcr``      Map NL to CR-NL on output
+``-onlcr``     Don't map NL to CR-NL
+``opost``      Enable output processing
+``-opost``     Disable output processing
+``isig``       Enable signal characters
+``-isig``      Disable signal characters
+``inlcr``      Map NL to CR on input
+``-inlcr``     Don't map NL to CR on input
+``igncr``      Ignore CR on input
+``-igncr``     Don't ignore CR on input
+``ocrnl``      Map CR to NL on output
+``-ocrnl``     Don't map CR to NL on output
+``speed N``    Set baud rate
+``min N``      Set VMIN (minimum chars for read, 0-255)
+``time N``     Set VTIME (read timeout in 0.1s, 0-255)
+=============  ==========================================
+
+Examples
+^^^^^^^^
+
+.. code-block:: bash
+
+   # Display current settings for /dev/ttyS0
+   nsh> stty -F /dev/ttyS0
+
+   # Set raw mode for binary communication
+   nsh> stty -F /dev/ttyS0 raw -echo
+
+   # Set cooked mode for interactive terminal
+   nsh> stty -F /dev/ttyS0 cooked
+
+   # Configure baud rate
+   nsh> stty -F /dev/ttyS1 speed 115200
+
+   # Set non-blocking read with timeout
+   nsh> stty -F /dev/ttyS0 min 0 time 10
+
+   # Display current settings for stdin
+   nsh> stty
+
+Configuration
+-------------
+
+**CONFIG_SYSTEM_STTY**
+
+Options:
+
+* **CONFIG_SYSTEM_STTY_PRIORITY** - Task priority (default 100)
+* **CONFIG_SYSTEM_STTY_STACKSIZE** - Stack size (default
+  ``DEFAULT_TASK_STACKSIZE``)
+
+Dependencies
+^^^^^^^^^^^^
+
+* **CONFIG_SERIAL_TERMIOS** - Required for termios support
+