Update broken links (#8589)

https://www.arduino.cc/en/main/software - broken
https://www.arduino.cc/en/software - working

README.md

@@ -28,7 +28,7 @@ ESP8266 Arduino core comes with libraries to communicate over WiFi using TCP and
 
 Starting with 1.6.4, Arduino allows installation of third-party platform packages using Boards Manager. We have packages available for Windows, Mac OS, and Linux (32 and 64 bit).
 
-- Install the current upstream Arduino IDE at the 1.8.9 level or later. The current version is on the [Arduino website](https://www.arduino.cc/en/main/software).
+- Install the current upstream Arduino IDE at the 1.8.9 level or later. The current version is on the [Arduino website](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.
 - 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).
@@ -43,7 +43,7 @@ Documentation: [https://arduino-esp8266.readthedocs.io/en/3.0.2/](https://arduin
 
 Also known as latest git or master branch.
 
-- Install the current upstream Arduino IDE at the 1.8 level or later. The current version is on the [Arduino website](https://www.arduino.cc/en/main/software).
+- Install the current upstream Arduino IDE at the 1.8 level or later. The current version is on the [Arduino website](https://www.arduino.cc/en/software).
 - Follow the [instructions in the documentation](https://arduino-esp8266.readthedocs.io/en/latest/installing.html#using-git-version).
 
 ### Using PlatformIO