dockerd-rootless.sh: add typo guard

`dockerd-rootless.sh install` is a common typo of `dockerd-rootless-setuptool.sh install`.

Now `dockerd-rootless.sh install` shows human-readable error.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>
(cherry picked from commit 8dc6c109b59b4f5629e7fb6018be88a068d1bad7)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

contrib/dockerd-rootless.sh

@@ -18,6 +18,12 @@
 # See the documentation for the further information: https://docs.docker.com/engine/security/rootless/
 
 set -e -x
+case "$1" in
+	"check" | "install" | "uninstall")
+		echo "Did you mean 'dockerd-rootless-setuptool.sh $@' ?"
+		exit 1
+		;;
+esac
 if ! [ -w $XDG_RUNTIME_DIR ]; then
 	echo "XDG_RUNTIME_DIR needs to be set and writable"
 	exit 1