update README

README.md

@@ -159,6 +159,17 @@ parser.onparsingerror = function(e) {
 };
 ```
 
+####ontimestampmap(timestampmap)####
+
+Is invoked when an `X-TIMESTAMP-MAP` metadata header ([defined here](https://tools.ietf.org/html/draft-pantos-http-live-streaming-20#section-3.5)) is parsed. This header maps WebVTT cue timestamps to MPEG-2 (PES) timestamps in other Renditions of the Variant Stream.
+
+```js
+parser.ontimestampmap = function(timestamp) {
+  console.log('LOCAL:', timestamp.LOCAL);
+  console.log('MPEGTS:', timestamp.MPEGTS);
+};
+```
+
 ####WebVTT.convertCueToDOMTree(window, cuetext)####
 
 Parses the cue text handed to it into a tree of DOM nodes that mirrors the internal WebVTT node structure of
@@ -538,18 +549,18 @@ for the task. If you want to know more about `cue2json` you can run it directly
 like so:
 
 ```bash
-$ ./bin/cue2json.js 
+$ ./bin/cue2json.js
 $ Generate JSON test files from a reference VTT file.
 $ Usage: node ./bin/cue2json.js [options]
-$ 
+$
 $ Options:
-$   -v, --vtt      Path to VTT file.                                                                                     
+$   -v, --vtt      Path to VTT file.
 $   -d, --dir      Path to test directory. Will recursively find all JSON files with matching VTT files and rewrite them.
-$   -c, --copy     Copies the VTT file to a JSON file with the same name.                                                
-$   -p, --process  Generate a JSON file of the output returned from the processing model. 
+$   -c, --copy     Copies the VTT file to a JSON file with the same name.
+$   -p, --process  Generate a JSON file of the output returned from the processing model.
 ```
 
-**Notes:** 
+**Notes:**
 
 * `cue2json` utilizes the last development build done. This is why the Grunt `run` task is
 good as you don't have to remember to build it yourself. If you don't build it yourself then you could