As was done indc7c6487cf(Makefile: check rootfs overlays with BR2_ROOTFS_MERGED_USR enabled) to document how overlays should be set up for the merged-usr case, and following428ac6fcc4(system: add support for merged /usr/sbin (aka merged-bin), extend the documentation to explain how rootfs overlays should be set up for the merged-bin case. Reported-by: Romain Naour <romain.naour@gmail.com> Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr> Signed-off-by: Julien Olivain <ju.o@free.fr>