Use the script above by making it executable (chmod +x convert.sh) and running it (./convert.sh).
If you want to add a page break use <<<, if you want to add syntax highlighting add :source-highlighter: rouge at the top of the Markdown file, it won't be rendered in Markdown but will be used by asciidoctor.
A very nice script for the conversion of markdown files. One minor comment, could you add quotes "$(pwd)" to the second docker command?