Update notes for 2.13 about deprecation of window.$

notes/2.13.md

@@ -7,3 +7,21 @@ Previously, objects generated by the library were given id properties with value
 Corresponding issues/pull requests:
 
  * https://github.com/openlayers/openlayers/pull/416
+ 
+# Behavior Changes from Past Releases
+
+## window.$ is no longer an alias for OpenLayers.Util.getElement
+ 
+We do no longer create a global variable '$' when such a symbol isn't already
+defined. Previous versions of OpenLayers would define '$' to be an alias for 
+OpenLayers.Util.getElement. If you application requires window.$ to be defined 
+in such a way you can either
+ 
+* include deprecated.js in your custom build or as additional ressource in your
+  HTML-file
+* or you do the aliasing in your application code yourself:
+    window.$ = OpenLayers.Util.getElement;
+    
+Corresponding issue/pull requests:
+
+* https://github.com/openlayers/openlayers/pull/423