docs: Radio is now turned on during import.

[microbit-carlos]

As discussed in:

• https://github.com/microbit-foundation/micropython-microbit-v2/issues/97
• https://github.com/bbcmicrobit/micropython/issues/760

And implemented in https://github.com/bbcmicrobit/micropython/commit/8d2138720fa2cdadbeebba8a8f0a72563b891f20 and https://github.com/microbit-foundation/micropython-microbit-v2/commit/ca108e7d609c14b1c2a6c2e895eb019056a3e92d.

Preview URLs:

• https://microbit-micropython--763.org.readthedocs.build/en/763/radio.html
• https://microbit-micropython--763.org.readthedocs.build/en/763/tutorials/radio.html