Declare 920Mhz as supported in docs, add Japan presets

[christianhorn]

• I think the code supports 868MHz ~ 923MHz, but the frontpage currently just mentions 868? The vendor mentions that range: https://docs.m5stack.com/en/cap/Cap_LoRa-1262 . Simple testing (a post in the 'public' channel) with a Heltec v3 (which does 920Mhz) worked fine.
• Please add presettings for Japan: 920.6Mhz, 62.5, 8, 8, 20mW. Source: https://qiita.com/ammo0613/items/d952154f1195b64dc29f .