Add link to component page

Just noticed that this was missing :) 

You're probably familiar with the GitHub publish flow for elements, but if not, my [publishing guide](https://www.polymer-project.org/docs/start/reusableelements.html#publishing-a-demo-and-landing-page-for-your-element) talks through using our scripts to push a nicely packaged version of your element to `gh-pages`.

I've done a quick push for this element that should be live here http://polymerlabs.github.io/site-search, but any further pushes will overwrite it so it stays fresh.