Let's consider that the very few people who still use DVD can figure
this out by themselves. And we can remove a few lines to read for
everybody else.

It's only inlined here.

It's mostly used in cloning scenarios that have no intermediary Tails.

Now it's only use in cloning scenarios.

So it better matches its content.

It's only used now in scenarios involving cloning: install-clone,
mac-clone, upgrade-clone, and upgrade-tails.

I'm reusing the text that we had on /install/mac/usb for using `dd`.
See 6b3f8325 or the current master branch.

The Oxford comma is for lists of 3 or more items.