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.
I'm okay with questions as titles, as long as we don't do it too often. Agree on down-casing "errors". The "no" should not be up-cased, however.