boards: arm: stm32h747i_disco: doc: images

add images for board ethernet modification
add index.rst Ethernet HW modifications description

Signed-off-by: Alexander Kozhinov <AlexanderKozhinov@yandex.com>

boards/arm/stm32h747i_disco/doc/index.rst

@@ -119,6 +119,33 @@ Default configuration assigns USART1 and UART8 to the CPU1. The Zephyr console
 output is assigned to UART1 which connected to the onboard ST-LINK/V3.0. Virtual
 COM port interface. Default communication settings are 115200 8N1.
 
+Ethernet
+========
+
+**Disclaimer:** This section is mostly copy-paste of corresponding
+`DISCO_H747I modifications for Ethernet`_ mbed blog post. The author of this
+article sincerely allowed to use the images and his knowledge about necessary
+HW modifications to get Ethernet working with this board.
+
+To get Ethernet working following HW modifications are required:
+
+- **SB21**, **SB45** and **R87** should be opened
+- **SB22**, **SB44**, **SB17** and **SB8** should be closed
+
+Following two images shows necessary changes on the board marked:
+
+.. image:: img/disco_h747i_ethernet_modification_1.jpg
+     :width: 271px
+     :align: center
+     :height: 596px
+     :alt: STM32H747I-DISCO - Ethernet modification 1 (**SB44**, **SB45**)
+
+.. image:: img/disco_h747i_ethernet_modification_2.jpg
+     :width: 344px
+     :align: center
+     :height: 520px
+     :alt: STM32H747I-DISCO - Ethernet modification 2 (**SB21**, **R87**, **SB22**, **SB17** and **SB8**)
+
 Resources sharing
 =================
 
@@ -242,3 +269,6 @@ You can debug an application in the usual way.  Here is an example for the
 
 .. _STM32CubeProgrammer:
    https://www.st.com/en/development-tools/stm32cubeprog.html
+
+.. _DISCO_H747I modifications for Ethernet:
+   https://os.mbed.com/teams/ST/wiki/DISCO_H747I-modifications-for-Ethernet