Makefile: check rootfs overlays with BR2_ROOTFS_MERGED_USR enabled
Add a step to target-finalize that checks each rootfs overlay, following
the criteria established for custom skeletons and using the same script
uesd by skeleton-custom.mk.
Add a paragraph to the documentation clarifying that rootfs overlays
don't need to contain /bin, /lib or /sbin and must not contain them when
BR2_ROOTFS_MERGED_USR is enabled.
Signed-off-by: Carlos Santos <casantos@datacom.ind.br>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>