use the newc archive format as requested by initramfs

This is a documentation followup to 2e591bbc

Signed-off-by: Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com>
Signed-off-by: Adrian Bunk <bunk@kernel.org>

Documentation/initrd.txt

@@ -85,7 +85,7 @@ involve special block devices or loopbacks; you merely create a directory on
 disk with the desired initrd content, cd to that directory, and run (as an
 example):
 
-find . | cpio --quiet -c -o | gzip -9 -n > /boot/imagefile.img
+find . | cpio --quiet -H newc -o | gzip -9 -n > /boot/imagefile.img
 
 Examining the contents of an existing image file is just as simple: