Add comment about line ending setting in the serial monitor

Author: sandeepmistry

libraries/SAMD_BootloaderUpdater/examples/UpdateBootloader/UpdateBootloader.ino

@@ -1,10 +1,12 @@
 /*
   Update Bootloader
 
-  This sketch checks if you Arduino SAMD board is running the latest bootloader.
+  This sketch checks if your Arduino SAMD board is running the latest bootloader.
 
   If it is not, it prompts you to update it.
 
+  NOTE: please make sure the line ending setting in the Serial Monitor is set to "Both NL & CR"
+
   Circuit:
   - MKR Vidor 4000