fixes in doc and playground

Author: thomaslule

README.md

@@ -69,6 +69,14 @@ The view is already refreshed when the user scrolls or resizes his window, but y
 
 Don't display the footnotes anymore, don't listen to the scroll and resize events anymore.
 
+#### addRefreshListener(listener)
+
+The function passed will be called each time the view is refreshed.
+
+#### removeRefreshListener(listener)
+
+The function passed won't be called anymore when the view is refreshed.
+
 ### Example
 
 ````javascript

playground/index.html

@@ -46,7 +46,7 @@ <h1>fixed-footnotes</h1>
   padding: 5px;
 }
 
-.fixed-footnotes-container.empty {
+.fixed-footnotes-container.fixed-footnotes-empty {
   display: none;
 }