Mercurial's documentation is kept in reStructuredText format, which is
a simple plain text format that's easy to read and edit:
http://docutils.sourceforge.net/rst.html
It's also convertible to a variety of other formats including standard
UNIX man page format and HTML.
To do this, you'll need to install the rst2html and rst2man tools,
which are part of Docutils:
http://docutils.sourceforge.net/
The rst2man tool is still in their so-called "sandbox". The above page
has links to tarballs of both Docutils and their sandbox.
Use the Makefile in this directory to generate the man and HTML pages.