EDIT: fixed link
EDIT: Your new link doesn't tell a different story. From the comments:
> It is still possible to disable secure boot using csrutil. Apple has never officially supported booting Linux on a Mac.
> https://twitter.com/never_released/status/127585087215369011...
Okay, so we can disable secure boot. What is the next step? How does one get to running Linux natively from there?