Update README.md

tried to add this in my latest arduino ide version and for whatever reason file > preferences isn't available. But pressing "cmd" +"," will bring up preferences

Author: sakifcho

README.md

@@ -30,7 +30,7 @@ Starting with 1.6.4, Arduino allows installation of third-party platform package
 
 - [Download and install Arduino IDE 1.x or 2.x](https://www.arduino.cc/en/software)
 - Start Arduino and open the Preferences window
-- Enter `https://arduino.esp8266.com/stable/package_esp8266com_index.json` into the *File>Preferences>Additional Boards Manager URLs* field of the Arduino IDE. You can add multiple URLs, separating them with commas.
+- Enter `https://arduino.esp8266.com/stable/package_esp8266com_index.json` into the *File>Preferences>Additional Boards Manager URLs OR you can press `command`+`,` on mac* field of the Arduino IDE. You can add multiple URLs, separating them with commas.
 - Open Boards Manager from Tools > Board menu and install *esp8266* platform (and don't forget to select your ESP8266 board from Tools > Board menu after installation).
 
 #### Latest release [![Latest release](https://img.shields.io/github/release/esp8266/Arduino.svg)](https://github.com/esp8266/Arduino/releases/latest/)