doc: develop: flash_debug: add realtek bee mpcli docs

Add setup and usage documentation for realtek bee mpcli.

Signed-off-by: Zophai Liu <zophai_liu@realsil.com.cn>

Author: zophai-liu

doc/develop/flash_debug/host-tools.rst

@@ -658,6 +658,28 @@ using the ``--device`` option:
 
 For more about the UF2 format and its tooling, see `USB Flashing Format (UF2)`_.
 
+.. _runner_mpcli:
+
+Realtek Bee Flash Programmer (MPCli) Host Tools
+***********************************************
+
+Realtek provides `Realtek Flash Programmer (MPCli)`_ as an official programming tool for the Bee
+series, supporting Linux, macOS, and Windows operating systems. MPCli enables In‑System Programming
+(ISP) via a UART interface, eliminating the need for external programming hardware. On most
+official Bee‑series evaluation boards, a built‑in UART‑to‑USB converter is included for
+ready‑to‑use programming and logging.
+
+After downloading the archive of MPCli, extract it and choose the version compatible with your
+operating system. Then, add the directory containing the ``mpcli`` executable to your system
+:ref:`PATH environment variable <env_vars>`.
+
+Before starting, ensure your board is in download mode. Please refer to the board documentation
+at: `Realtek Supported Boards`_
+
+.. code-block:: console
+
+   west flash [--runner mpcli] --port /dev/ttyX
+
 .. _J-Link Software and Documentation Pack:
    https://www.segger.com/downloads/jlink/#J-LinkSoftwareAndDocumentationPack
 
@@ -735,3 +757,9 @@ For more about the UF2 format and its tooling, see `USB Flashing Format (UF2)`_.
 
 .. _USB Flashing Format (UF2):
    https://github.com/microsoft/uf2
+
+.. _Realtek Flash Programmer (MPCli):
+   https://docs.realmcu.com/tools/mpcli_tool/en/latest/mpcli/text_en/README.html
+
+.. _Realtek Supported Boards:
+   https://docs.zephyrproject.org/latest/boards/realtek/index.html