freebsd.md: add section on using life preserver from PC-BSD

Signed-off-by: Andrew Turner <andrewjamesturner0@gmail.com>
arch.md: add UEFI instructions for grub

Signed-off-by: Andrew Turner <andrewjamesturner0@gmail.com>
arch.md: add section on laptop powersaving options

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