[STM32MP157_DK] Update root README.md to add this variant

Author: kbumsik

README.md

@@ -148,6 +148,11 @@ User can add a STM32 based board following this [wiki](https://github.com/stm32d
 | :---: | --- | :---: | :--- |
 | :green_heart: | [SharkyMKR](https://midatronics.com/Development_Boards/MKR_Sharky_I) | *1.7.0* |  |
 
+| Status | [STM32MP1 Dev Kit](https://github.com/stm32duino/Arduino_Core_STM32/tree/master/variants/STM32MP157_DK/README.md) | Release | Comment |
+| :---: | --- | :---: | :--- |
+| :yellow_heart: | [STM32MP157A-DK1](https://github.com/stm32duino/Arduino_Core_STM32/tree/master/variants/STM32MP157_DK/README.md) | *1.1.0* | See [the documentation](https://github.com/stm32duino/Arduino_Core_STM32/tree/master/variants/STM32MP157_DK/README.md) to use this board|
+| :yellow_heart: | [STM32MP157C-DK2](https://github.com/stm32duino/Arduino_Core_STM32/tree/master/variants/STM32MP157_DK/README.md) | *1.1.0* | See [the documentation](https://github.com/stm32duino/Arduino_Core_STM32/tree/master/variants/STM32MP157_DK/README.md) to use this board|
+
 ## Next release
 
   See [milestones](https://github.com/stm32duino/Arduino_Core_STM32/milestones) to have an overview of the next release content.