added link button for newly launched stats.bower.io

Per work at https://github.com/bower/bower/issues/1164.

Even though readme says to edit template instead of index.html directly, I see that index.html was edited manually a few times already, and is already out of sync from the readme.md in bower's repo. To minimize impact of this commit I didn't want to bundle in bringing homepage in sync with bower's readme.md. At this point it may not be worth it to bring it in sync per switching to jekyll here: https://github.com/bower/bower.github.io/issues/4