docs/website/news.html: add 2015.05-rc1 announcement link

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

docs/website/news.html

@@ -13,7 +13,8 @@
     <p>We have a new release candidate! Lots of changes all over the
     tree, see the <a
     href="http://git.buildroot.net/buildroot/plain/CHANGES?id=2015.05-rc1">CHANGES</a>
-    file for details.</p>
+    file for details, and read the
+    <a href="http://lists.busybox.net/pipermail/buildroot/2015-May/127794.html">announcement</a>.</p>
 
     <p>Head to the <a href="/downloads/">downloads page</a> to pick up the
     <a href="/downloads/buildroot-2015.05-rc1.tar.bz2">2015.05-rc1