Help people:

- Understand when Wi-Fi is not working.
- Find a workaround in the known_issues.
- Find a USB Wi-Fi adapter that works.

Inline these instructions in the 3 places where they make more sense:

- When starting Tails for the first time.
- In the NetworkManager documentation.
- In the Wi-Fi section of the known issues.

I'm commenting out some USB adapters that work but that don't really
have advantages over the ones that are listed already.