Update boards_manager.md (espressif#5296)

Author: Leziga-Bakor

docs/arduino-ide/boards_manager.md

@@ -9,4 +9,4 @@ Starting with 1.6.4, Arduino allows installation of third-party platform package
 - Install the current upstream Arduino IDE at the 1.8 level or later. The current version is at the [Arduino website](http://www.arduino.cc/en/main/software).
 - Start Arduino and open Preferences window.
 - Enter one of the release links above into *Additional Board Manager URLs* field. You can add multiple URLs, separating them with commas.
-- Open Boards Manager from Tools > Board menu and install *esp32* platform (and don't forget to select your ESP32 board from Tools > Board menu after installation).
+- Open Boards Manager from Tools > Board menu and install *esp32* platform (and do not forget to select your ESP32 board from Tools > Board menu after installation).