Update README.md

Author: fpistm

README.md

@@ -1,5 +1,7 @@
 # Arduino core support for STM32 based boards
-### Latest release [![GitHub release](https://img.shields.io/github/release/stm32duino/Arduino_Core_STM32.svg)](https://github.com/stm32duino/Arduino_Core_STM32/releases/latest) [![GitHub commits](https://img.shields.io/github/commits-since/stm32duino/Arduino_Core_STM32/2018.1.18.svg)](https://github.com/stm32duino/Arduino_Core_STM32/compare/2018.1.18...master)
+### Latest release [![GitHub release](https://img.shields.io/github/release/stm32duino/Arduino_Core_STM32.svg)](https://github.com/stm32duino/Arduino_Core_STM32/releases/latest) [![GitHub commits](https://img.shields.io/github/commits-since/stm32duino/Arduino_Core_STM32/1.1.1.svg)](https://github.com/stm32duino/Arduino_Core_STM32/compare/1.1.1...master)
+
+**Warning**: release versioning has been changed from date versioning to semantic one. See [Release Versioning change](https://github.com/stm32duino/wiki/wiki/Release-Versioning-change)
 
 * [Getting Started](https://github.com/stm32duino/Arduino_Core_STM32#getting-started)<br>
 * [Boards available](https://github.com/stm32duino/Arduino_Core_STM32#boards-available)<br>