Would you mind adding a "Visit arRsync Web Site" item to the Help menu that would perform the obvious action? I would like to see this become more of a trend (see, e.g., Camino, Vienna, Skim, and BibDesk).
(As an aside, some might argue that you should not even have a help menu if its sole function is to inform the user that "Help isn't available for arRsync.")