Xubuntu 18.04 on Lenovo T500: Wifi Intel 5100

[^rooker]

[PROBLEM]
Disclaimer: The T500 works flawlessly on Bionic Beaver (18.04)
Including Full-HD playback in the browser. Out of the box.

I must embarrassingly admit that I just spent 20 minutes debugging the wifi interface not showing up in NetworkManager on Xubuntu 18.04.
I got weird error messages like:

iwlist scan:

interface doesn't support scanning network is down

ifconfig up:

operation not possible due to RF-kill

[SOLUTION]
$ rfkill list

soft blocked: no
hard blocked: yes

Eeee...
The T500 has a hardware switch to disable/enable the wireless hardware.