Update "scratch" and "hello-world" to be more complimentary

hello-world/update.sh

@@ -18,3 +18,10 @@ echo
 
 echo
 echo '%%LOGO%%'
+
+echo
+cat <<'EOF'
+# How is this image created?
+
+This image is a prime example of using the [`scratch`](https://registry.hub.docker.com/_/scratch/) image effectively. See [`hello.asm`](%%GITHUB-REPO%%/blob/master/hello.asm) in %%GITHUB-REPO%% for the source code of the `hello` binary included in this image.
+EOF

scratch/README.md

@@ -1,5 +1,5 @@
 # `FROM scratch`
 
-This image is most useful in the context of building base images or super minimal images (such as images that contain only a single binary; see [`hello-world`](https://github.com/docker-library/hello-world) for an example).
+This image is most useful in the context of building base images (such as [`debian`](https://registry.hub.docker.com/_/debian/) and [`busybox`](https://registry.hub.docker.com/_/busybox/)) or super minimal images (that contain only a single binary and whatever it requires, such as [`hello-world`](https://registry.hub.docker.com/_/hello-world/)).
 
-As of Docker 1.5.0 (specifically, [`docker/docker#8827`](https://github.com/docker/docker/pull/8827)), `FROM scratch` is a no-op in the `Dockerfile`, and will not create an extra layer in your image (so a previously 2-layer image will now be a 1-layer image instead).
+As of Docker 1.5.0 (specifically, [`docker/docker#8827`](https://github.com/docker/docker/pull/8827)), `FROM scratch` is a no-op in the `Dockerfile`, and will not create an extra layer in your image (so a previously 2-layer image will be a 1-layer image instead).