With a lot of similarly named boards, be more specific about the supported boards

[tigert]

Describe the bug
We list these as supported boards:

• Arduino Mega
• Arduino Mega Pro Mini
• Arduino Pro Micro
• Arduino Uno
• Arduino Nano

Of these "Nano" and "Uno" at least are confusing since there are now 17 different variants (!) of Arduino Nano on the official site, and also several variants of Uno that are not supported.

Fortunately there is only the supported kind of Mega and Mega mini.

But for Uno and Nano we should list "Arduino Uno R3" and "Arduino Nano R3" to rule out all the ESP32 and RP2040 variants (that kinda do work as pico, but that is another story)