Add a note on EEPROM todo

Marlin/src/HAL/shared/eeprom_i2c.cpp

@@ -23,6 +23,9 @@
 /**
  * Description: functions for I2C connected external EEPROM.
  * Not platform dependent.
+ *
+ * TODO: Some platform Arduino libraries define these functions
+ *       so Marlin needs to add a glue layer to prevent the conflict.
  */
 
 #include "../../inc/MarlinConfig.h"