netpkt: Introduction to using netpkt example

The introduction includes an overview, the configuration items that need to be enabled, and how to use them.

Signed-off-by: zhangshuai39 <zhangshuai39@xiaomi.com>

Documentation/applications/examples/netpkt/index.rst

@@ -3,3 +3,49 @@
 ====================================
 
 A test of ``AF_PACKET``, raw sockets. Contributed by Lazlo Sitzer.
+
+Overview
+========
+
+The ``netpkt`` example demonstrates the use of raw packet sockets (``AF_PACKET``)
+for sending and receiving Ethernet frames at the link layer, bypassing the
+TCP/IP protocol stack. This is useful for network protocol testing, driver
+verification, and low-level network analysis.
+
+Configuration
+=============
+
+- ``CONFIG_EXAMPLES_NETPKT=y`` – Enables the netpkt example.
+
+Usage
+=====
+
+The ``netpkt`` program supports the following command-line options:
+
+.. code-block:: bash
+
+   netpkt [options]
+
+Options:
+
+- ``-a`` – Transmit and receive packets
+- ``-r`` – Receive packets only
+- ``-t`` – Transmit packets only
+- ``-v`` – Verbose mode (display packet contents in hexadecimal)
+- ``-i <IF>`` – Specify network interface name (e.g., ``eth0``)
+
+Examples:
+
+.. code-block:: bash
+
+   # Send 3 packets on eth0 interface with verbose output
+   netpkt -i eth0 -t -v
+
+   # Receive packets on eth0 interface
+   netpkt -i eth0 -r -v
+
+   # Both send and receive on eth0
+   netpkt -i eth0 -a -v
+
+   # Send packets without specifying interface (uses default)
+   netpkt -t