[yocto] Create empty directory in RFS

[Edward Wingate]

How can I create an empty directory in my root FS?  I want to create
/mnt/sd to use as a mount point.  I put "install -d ${D}/mnt/sd" in
do_install() of one of my recipes, but I get:

ERROR: QA Issue: my-recipe: Files/directories were installed but not shipped
  /mnt
  /mnt/sd [installed-vs-shipped]

Thanks for any help.