This documentation is included in the TM5 distribution in the 'doc/tex/' directory.
To contribute to the documentation, simply change the appropriate files. A local version of the documentation could be generated by:
TM5/doc/tex $ make html
To have your changes exported to the web site, first commit to the cvs server, e.g.
TM5/doc/tex $ cvs commit -m 'Added description of latest changes.' tm5.texOnce every day around 5:00 UTC, an up-to-date version of the documentation will be extracted automatically from the cvs server, converted to html, and copied to the web server.