Add placehold.co to websites list

websites.html

@@ -50,7 +50,8 @@
 					<li><a href="https://vecta.io/nano" target="_blank" rel="noopener">vecta.io/nano</a></li>
 					<li><a href="https://tinypng.com/" target="_blank" rel="noopener">tinypng.com</a></li>
 					<li><a href="https://webaim.org/resources/contrastchecker/" target="_blank" rel="noopener">webaim.org/resources/contrastchecker/</a></li>
-					<li><a href="https://via.placeholder.com/" target="_blank" rel="noopener">via.placeholder.com</a> - <a href="https://via.placeholder.com/320x480/" target="_blank" rel="noopener">example</a></li>
+					<li><a href="https://via.placeholder.com/" target="_blank" rel="noopener">via.placeholder.com</a> (raster) - <a href="https://via.placeholder.com/320x480/" target="_blank" rel="noopener">example</a></li>
+					<li><a href="https://placehold.co" target="_blank" rel="noopener">placehold.co</a> (vector) - <a href="https://placehold.co/768x384" target="_blank" rel="noopener">example</a></li>
 				</ul>
 			</section>