Update encrypted volumes creation documentation to Jessie's GNOME Disks
Originally created by @sajolida on #8048 (Redmine)
Disks now creates a LUKS+Ext4 volume with one widget.
Feature Branch: doc/8048-encrypted-volumes
Parent Task: #8043 (closed)
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information