README: Link to the new openSUSE package

On Sat, Mar 02, 2013 at 08:54:11AM -0800, Arun Persaud wrote:
> I managed to get rss2email 3.1 packaged for opensuse. It's available at
>
> http://download.opensuse.org/repositories/server:/mail/
>
> for 12.2, 12.3 and Factory in case you want to mention it on the project
> page. It doesn't build on older distros, mostly due to missing
> dependencies, but on 12.1 the build fails with
>
> ...
>
> The package is developed at:
>
> https://build.opensuse.org/package/show?package=rss2email&project=server%3Amail

Signed-off-by: W. Trevor King <wking@tremily.us>