add section in README re:withCredentials

@@ -49,6 +49,19 @@ support for:
 - Segment codecs _other than_ H.264 with AAC audio
 - Internet Explorer < 10
 
+### Plugin Options
+
+You may pass in an options object to the hls plugin upon initialization. This
+object may contain one of the following properties:
+
+#### withCredentials
+Type: `boolean`
+
+When the `withCredentials` property is set to `true`, all XHR requests for
+manifests and segments would have `withCredentials` set to `true` as well. This
+enables storing and passing cookies from the server that the manifests and
+segments live on.
+
 ### Runtime Properties
 #### player.hls.master
 Type: `object`