[Discuss-gnuradio] A small tweak to the project homepage

[Benjamin J. Tarval]

Normally I wouldn't bother mentioned such a small change, but this 
might prove handy if you're trying to locate the mailling list archives.

I've put a link to the web-based archives on the gnuradio project homepage.
So if you want to get there, just go to http://www.gnu.org/software/gnuradio/
and check out the section on "Mailling lists and contacts" at the bottom
of the page.

        -ben-