Updated link to sample app (#5)

* Updated link to sample app (using play store instead of legacy google market link)

* Update link description to synchronise with link and google products naming

README.TXT

@@ -1,5 +1,5 @@
 This project is a repository for the lessons and tutorials over at http://www.learnopengles.com/
 
-The compiled app can be downloaded from the Android market at https://market.android.com/details?id=com.learnopengles.android
+The compiled app can be downloaded from the Google Play Store (originally the Android market) at https://play.google.com/store/apps/details?id=com.learnopengles.android
 
 The WebGL tutorials can be viewed at http://www.learnopengles.com/