add bitcoin donate button

index.html

@@ -76,7 +76,9 @@
       <a href="https://twitter.com/share" class="twitter-share-button" data-text="Check out 2048, a game where you join numbers to score high! #2048game" data-via="gabrielecirulli">Tweet</a>
       <script>!function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0],p=/^http:/.test(d.location)?'http':'https';if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src=p+'://platform.twitter.com/widgets.js';fjs.parentNode.insertBefore(js,fjs);}}(document, 'script', 'twitter-wjs');</script>
       <span class="btc-donate">
-        <img src="meta/icon_bitcoin.png">Donate
+        <a href="bitcoin:1Ec6onfsQmoP9kkL3zkpB6c5sA4PVcXU2i">
+          <img src="meta/icon_bitcoin.png">Donate
+        </a>
         <span class="address"><code>1Ec6onfsQmoP9kkL3zkpB6c5sA4PVcXU2i</code></span>
       </span>
     </div>