[archiso] Document needed pkgs required to build

Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>

README

@@ -7,6 +7,7 @@ INDEX
   * hooks/archiso_loop_mnt
 * Boot parameters (only for configs/releng)
   * etc/rc.conf
+* Build requirements
 * Image types generated by mkarchiso.
 * File format for aitab.
 * Why the /isolinux and /arch/boot/syslinux directories?
@@ -87,6 +88,25 @@ if nothing is specified on command line.
 
 
 
+*** Build requirements
+
+** For mkarchiso script needs these packages (build host):
+ + devtools                for mkarchroot
+ + squashfs-tools          for mksquashfs
+ + syslinux                for isohybrid
+ + cdrkit                  for mkisofs
+
+** For these hooks needs these packages (on target root-image)
+* archiso
+ + (none)
+* archiso_loop_mnt
+ + (none)
+* archiso_pxe_nbd
+ + mkinitcpio-nfs-utils    for ipconfig
+ + nbd                     for nbd-client
+
+
+
 *** Image types generated by mkarchiso.
 
 * image-name.sfs     SquashFS image with all files directly on it.