Docudown is a Lisp documentation tool built on top of CL-Markdown.
The easiest way to get setup with CL-Markdown is by using ASDF-Install. If that doesn't float your boat, there is a handy gzipped tar file and a darcs repository. The darcs commands to retrieve the
docudown source is:
darcs get "http://common-lisp.net/project/docudown"
(note that this won't let you build
docudown unless you also get all of its dependencies...)