Doc: Resizing Boot2Docker Volume with VirtualBox

The Boot2Docker VM ships with a 20G VMDK volume, which can quickly fill up if one is using large images/large numbers of images. This is a step-by-step guide for increasing the B2D volume using VirtualBox and GParted.
My reasoning is that since B2D is currently reliant upon VirtualBox, we're working within the constraints of that application. As such, the partitioning tool can only be used as a bootable ISO.