Update README.md

Author: iregon

README.md

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 # ACO - Arduino Code Optimizer
-Reduce memory usage of your Arduino sketch up to 90%.
+Reduce the memory usage of your Arduino sketch up to 90% by using the [Arduino Port Manipulation](https://www.arduino.cc/en/Reference/PortManipulation).
+
+All references to the ports used by the microcontroller can be found in its datasheet, e.g. [Atmega328P](http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-7810-Automotive-Microcontrollers-ATmega328P_Datasheet.pdf).
 
 **Attention: the use of this tool on your sketch could make it to lose portability between the different Arduino microcontrollers**