Improve wiki "Where are sources"

[thernstig]

Reference: https://github.com/stm32duino/Arduino_Core_STM32/wiki/Where-are-sources

The wiki says:

The location is displayed in the "Preferences" dialog.

This is not true. The preferences dialog contains the location for where the Sketchers are saved, but not where the installation of the various packages/platforms exist.

See here:

In addition, the wiki should add Windows 11 to this part:

c:\Users\\<USERNAME\>\AppData\Local\Arduino15\

Actually, you should just mention Windows 10 and Windows 11 and those locations, as previous version are not supported for Arduino 2.0, see here https://forum.arduino.cc/t/ide-2-2-1-compatibility-to-windows-8-1-64-bit/1201679.