Documentation for the new option.

Author: Julian Xhokaxhiu

README.md

@@ -69,6 +69,7 @@ afterOpen: null, // called after opening
 afterClose: function(){}, // called after closing
 loopAtEnd: false, // true will return to the first image after the last image is reached
 autoplayVideos: false // true will autoplay Youtube and Vimeo videos
+queryStringData: {} // plain object with custom query string arguments to pass/override for video URLs
 ```
 
 ###Pull Requests