Information re: STM32Duino support is outdated

[per1234]

The readme contains this statement:

Arduino_Alvik/README.md

Line 22 in 43f2951

Since this [issue](https://github.com/stm32duino/Arduino_Core_STM32/issues/2292), Arduino® Alvik Carrier is not integrated yet into STM32duino's boards.

However, the linked issue was resolved and a new release of the "STM32Duino" boards platform containing the change released a year ago.

So it appears that the information in the readme is now outdated.

[gbr1]

@per1234 yes, we should try adding Alvik Carrier into selectable boards in stm32duino

[gbr1]

@per1234 I changed the readme