Add a warning about the preinstalled devices on the download page
Originally created by @AtomiKe on #10415 (Redmine)
There are a lot of sellers who sell Tails shipped on preinstalled
devices (CD, USB keys, …). It’s not really a good practice.
We should add a warning on the download page and link it to the FAQ.
https://tails.boum.org/support/faq#index11h2