dded xz compression notes so that kernel can decompress.
dded xz compression notes so that kernel can decompress.

The kernel has some restrictions to decompress xz files. See
Documentation/xz.txt.

As initramfs.xz is embedded in the firmware file for Linuxboot
it is highly suggested to follow this recommendation

Signed-off-by: Francois-Frederic Ozog <ed70c57d7564e994e7d5f6fd6967cea8b347efbc@ozog.com>

u-root/u-root,hugelgupf/u-root,u-root/u-root,u-root/u-root,GanShun/u-root,rminnich/u-root,hugelgupf/u-root,hugelgupf/u-root,GanShun/u-root,rminnich/u-root,rminnich/u-root,rminnich/u-root,hugelgupf/u-root,GanShun/u-root