Docs: New-shield guide Metadata section should list some well-known interconnects

[amacleod]

Currently https://zmk.dev/docs/development/hardware-integration/new-shield#metadata shows a simple example of the requires: field in my_keyboard.zmk.yml, a Hardware Metadata file, showing [pro_micro] as the required interconnect. However, it does not mention any of the others by name.

As a first-time shield builder, I know from context and community that interconnects exist and roughly what they are, but not in enough detail to know their specific names as they should appear in a requires: clause in metadata. A little bit of hand-holding would go a long way in that section.

Expand the description of the metadata example to point out a few more well-known interconnects, like seeed_xiao and arduino_uno and, if reasonable, point readers at how to look up the names of others.

[amacleod]

Even a link to https://github.com/zmkfirmware/zmk/tree/main/app/boards/interconnects could help intermediate quasi-newbies like me orient themselves 😃

[amacleod]

Since https://github.com/zmkfirmware/zmk/tree/main/app/boards/interconnects mentions Arduino Uno, Blackpill, Pro Micro, and Seeed XIAO, maybe those would be a good list to include in the metadata section.

[amacleod]

Opened #2563 as a potential fix