Enhancement: support `west sdk` for use in the README

[beriberikix]

Currently in main, Zephyr introduced a much simpler way to install the SDK. Starting from zephyrproject-rtos/zephyr@b68071d you can simply run:

west sdk install --version 0.16.8

I think it would require updated the branch on the zephyr fork to at least that revision and then update the README.

Cheers!

[facchinm]

Great! We are preparing to move zephyr's head to 4.0+ , once done the fixing the documentation will make everything easier!