[Tails-ux] documentation installation guide MAC

Hi,

>
> sajolida:
> Spencer said sudo
>

I think it is necessary to explain the difference between /dev/disk# and
/dev/rdisk#, since the results of querying will display a list of
/dev/disk#.

A link:
http://serenity.ee/post/82120938429/mac-os-dd-with-devdisk-vs-devrdisk

Wordlife,
Spencer