admin/vm: start writing documentation of virtual machine

Just align fix, I hate TAB!!!

Signed-off-by: Dunrong Huang <riegamaths@gmail.com>
admin/vm: finish introducing what is virtual machine

Signed-off-by: Dunrong Huang <riegamaths@gmail.com>
admin/vm: finish 8.2 Supported Virtual Machine Operating Systems

Signed-off-by: Dunrong Huang <riegamaths@gmail.com>