note on tiled tiff read
note on tiled tiff read

I had a quick go at making tiffload shut down early for tiled tiff read,
but it's not really possible because tiled read is not guaranteed to be
ordered.

Add a note for future reference.

jcupitt/libvips,lovell/libvips,lovell/libvips,jcupitt/libvips,lovell/libvips,jcupitt/libvips,lovell/libvips,jcupitt/libvips