add audio autoplay test

test/examples/assets/beeping.txt

@@ -0,0 +1,2 @@
+Source: https://freesound.org/people/fennelliott/sounds/379419/
+License: CC0 (public domain)

test/examples/embedded-media.html

@@ -30,6 +30,11 @@
 					<h2>Empty Slide</h2>
 				</section>
 
+				<section>
+					<h2>Auto-playing audio</h2>
+					<audio src="assets/beeping.wav" data-autoplay></audio>
+				</section>
+
 			</div>
 
 		</div>