info 'bout which elems use which mode

Author: ryanve

README.md

@@ -176,4 +176,13 @@ Tip: use [jsonlint.com](http://jslint.com/) to make sure JSON is valid.
         prefix: "src",  // the prefix for your custom data attributes
         breakpoints: [1281,1025,961,641,481,320,0] // array of (min) breakpoints
     }])
-```
+```
+
+Since version 0.3.0:
+
+img|input|source|embed|track elements always behave in src mode.
+
+iframe|audio|video elements behave in src mode only when the src attribute is present. Otherwise they 
+use markup mode.
+
+All other elements behave in markup mode.