Add Play store link

Author: Sander Mak

index.html

@@ -298,7 +298,7 @@ <h3>eBook</h3>
 						<ul>
 							<li><span>DRM-Free PDF/ePub</span> <a href="http://bit.ly/java9mod-ebooks" target="_blank">ebooks.com</a></li>
 							<li><span>Kindle</span> <a href="http://amzn.to/2xgQ7qT" target="_blank">Amazon.com</a></li>
-							<li><span>PDF/ePub</span> <a target="_blank">Google Play Store (n/a yet)</a></li>
+							<li><span>PDF/ePub</span> <a href="https://play.google.com/store/books/details/Sander_Mak_Java_9_Modularity?id=LZQ0DwAAQBAJ" target="_blank">Google Play Store</a></li>
 						</ul>
 						<img src="img/java9modularity-cover-ereaderlaptop.jpg" width="240px">
 					</div>