For format, guidelines and planning see the documentation planning.
The documentation is made available on http://symfony.com/doc/master/cmf/index.html and is regenerated automatically whenever a change is pushed to the master branch on github.
In order to render this documentation locally follow the guidelines on http://readthedocs.org
In short the documentation requires the python tool Sphinx (note not the search engine daemon Sphinx)
to be installed and then generating the documentation should simply require running make html.
After making changes to the docs, it normally takes about 15min for them to appear on the website. Please also review the error log for problems http://symfony.com/doc/build_errors.