added missing comma on the configuration example

README.md

@@ -174,7 +174,7 @@ Reveal.initialize({
 	parallaxBackgroundImage: '', // e.g. "'https://s3.amazonaws.com/hakim-static/reveal-js/reveal-parallax-1.jpg'"
 
 	// Parallax background size
-	parallaxBackgroundSize: '' // CSS syntax, e.g. "2100px 900px"
+	parallaxBackgroundSize: '', // CSS syntax, e.g. "2100px 900px"
 
 	// Amount to move parallax background (horizontal and vertical) on slide change
 	// Number, e.g. 100