just upload a file to the CMS as described here and link apropriatly.
please use relative links, as this website runs different virtual hosts (e.g. "pure-data.info" or the deprecated puredata.org) and different protocols ("http" and "https")
if you are using structured text for markup create links as:
"linkname":/path/to/my/site
instead of complete URLs, such as:
"explicitURL":http://puredata.info/path/to/your/site