Accept donations via Bitcoin Cash

Someone asked if we have a BCH address. Turns out our Bitcoin address is old enough to function as a BCH address too.

content/_index.html

@@ -29,5 +29,5 @@ rel="noopener noreferrer">
 <a href="https://flattr.com/t/592836/" rel="noopener noreferrer">
 <img src="img/flattr-badge-large.png" alt="Flattr this" title="Flattr this"></a>
 <br>
-Bitcoin: 1NZCKkUCtJV2U2Y9hDb9uq8S7ksFCFGR6K
+Bitcoin and BCH: 1NZCKkUCtJV2U2Y9hDb9uq8S7ksFCFGR6K
 </div> <!-- flattr -->