Update README.md

Fix stm32duino#471

Author: fpistm

README.md

@@ -126,10 +126,16 @@ User can add a STM32 based board following this [wiki](https://github.com/stm32d
 
 ## Troubleshooting
 
+### Important notice:
+Previously, support was performed on [stm32duino forum](http://stm32duino.com). This forum, will be be read only from **Saturday 27th April**. User registration is no more possible. Further information [here](http://stm32duino.com/viewtopic.php?f=16&t=4540).
+
 If you have any issue, you could [file an issue on Github](https://github.com/stm32duino/Arduino_Core_STM32/issues/new).
 
-Or submit a topic on the [stm32duino forum](http://stm32duino.com):
+If you already have an account on [stm32duino forum](http://stm32duino.com), you can always submit a topic on the [stm32duino forum](http://stm32duino.com) until the _Saturday 27th April_:
 
  * questions on the [STM32 Core](http://stm32duino.com/viewforum.php?f=48)
-
+ 
  * bugs/enhancements on the [STM core: Bugs and enhancements](http://stm32duino.com/viewforum.php?f=49)
+
+In any case, it always fine to search on those topics before submit an issue.
+**We are currently working on finding the best handover solution.**