Update README.md

Co-authored-by: per1234 <[email protected]>

Author: facchinm

README.md

@@ -70,7 +70,7 @@ cd $sketchbook/hardware/arduino-git/mbed
 
 `-r` flag allows using a custom `mbed-os` fork in place of the mainline one; useful during new target development.
 
-**Adding a new target (variant)**
+### Adding a new target ([core variant](https://arduino.github.io/arduino-cli/latest/platform-specification/#core-variants))
 
 Adding a target is a mostly automatic procedure.