Add an additional clarifying note to the top of the per-architecture repositories

This was the result of some great feedback from David Messina that it's not obvious when a user lands on a page like https://hub.docker.com/r/arm32v7/docker that it's actually an official part of the official images program, and there isn't an obvious/consistent link *back* to the primary manifest-listed library image, which users should typically prefer to use if their platform/environment supports doing so.

update.sh

@@ -125,6 +125,12 @@ for image in "${images[@]}"; do
 		{
 			cat "$helperDir/autogenerated-warning.md"
 			echo
+
+			if [ -n "$ARCH_SPECIFIC_DOCS" ]; then
+				echo '**Note:** this is the "per-architecture" repository for the `'"$BASHBREW_ARCH"'` builds of [the `'"$repo"'` official image](https://hub.docker.com/_/'"$repo"') -- for more information, see ["Architectures other than amd64?" in the official images documentation](https://github.com/docker-library/official-images#architectures-other-than-amd64) and ["An image'\''s source changed in Git, now what?" in the official images FAQ](https://github.com/docker-library/faq#an-images-source-changed-in-git-now-what).'
+				echo
+			fi
+
 			echo -n "$deprecated"
 			cat "$helperDir/template.md"
 		} > "$targetFile"