Adapt installation instructions to the Jessie version of Tails Installer

Until Tails Jessie is out, we’ll have the old installer in Tails but then at least the wording and screenshot will change in Tails Jessie.

Feature Branch: web/10408-jessie-installer

Original created by @sajolida on 10408 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information