update readme for recurring events

README.md

@@ -17,6 +17,22 @@ Simply use invoke the object and use the functions...
 `begin` and `end` need to be formatted in a way that is friendly to `Date()`
 
 
+Recurring Events
+----------------
+Recurring events can be added with the `rrule` object.
+
+`cal.addEvent(subject, description, location, begin, end, rrule)`
+
+The `rrule` object has the following properties:
+
+- `freq` : __Required.__ The frequency of event recurrence. Can be `DAILY`, `WEEKLY`, `MONTHLY`, or `YEARLY`.
+- `until` : A date string representing the date on which to end repitition.  Must be friendly to `Date()`
+- `count` : Alternative to until.  Repeat the event `count` times.  Must be an integer
+- `interval` : The interval of `freq` to recur at.  For example, if `freq` is `WEEKLY` and `interval` is `2`, the event will repeat every 2 weeks.  Must be an integer.
+
+The four properties described above are not exhaustive of recurrence rule capabilities.  If extra functionality is required, you can set the `rrule.rule` property to a full recurrence rule string.  In this case, none of the four properties described above are necessary.  See [this page](http://www.kanzaki.com/docs/ical/rrule.html) for a description of recurrence rules.
+
+
 Example
 -------
 * **[Demo](http://htmlpreview.github.io/?https://github.com/nwcell/ics.js/blob/master/demo/demo.html)**