Separate notes for setting up VirtualBox from devnotes.md

Moves notes about setting up VirtualBox and about setting up the opal
virtual servers into separate files

Signed-off-by: Andrew Turner <andrewjamesturner0@gmail.com>
vmnotes.md: add section on importing and verifying the VMs

Signed-off-by: Andrew Turner <andrewjamesturner0@gmail.com>
gitnotes.md: Add notes about how to use git for DataSHIELD development

Signed-off-by: Andrew Turner <andrewjamesturner0@gmail.com>
Add Makefile for generating html files

Signed-off-by: Andrew Turner <andrewjamesturner0@gmail.com>