Add rationale for adding the alias

Author: sebromero

cores/arduino/Arduino.h

@@ -74,6 +74,8 @@ extern "C"{
 
 #define interrupts()        __enable_irq()
 #define noInterrupts()      __disable_irq()
+
+//Provide an alias for force-booting the M4 that is easy to remember
 #define bootM4() LL_RCC_ForceCM4Boot()
 
 // We provide analogReadResolution and analogWriteResolution APIs