Reading rd-files

Hello,

I'm using Ruby-GNOME2. The reference of the API is available on the
internet, but I would like to read it off-line. There's a tarball
available of the reference in RD format. But...

How do I read those files? Can I convert them easely to .html-files
(or other formats)? There's little info directly findable on the
internet...

Many thanks in advance!

Happy Rubying,
Cheers,
David