Updated README

Author: jhdavids8

readme.md

@@ -2,6 +2,51 @@ Chart.js
 =======
 *Simple HTML5 Charts using the canvas element* [chartjs.org](http://www.chartjs.org)
 
+## Changes
+This adds a mouseover and mouseout event to the data points in a line graph (events for all graphs may follow shortly). I implemented because I needed to implement tooltips for the data points, but you can use the event to do whatever you like.
+
+To hook into the events, just specify a mouseover and mouseout event handler for your dataset. This works for browser mouse events as well as mobile touch events.
+```javascript
+var data = {
+  labels : labels,
+  datasets : [
+    {
+      fillColor : "rgba(151,187,205,0.5)",
+      strokeColor : "rgba(151,187,205,1)",
+      pointColor : "rgba(151,187,205,1)",
+      pointStrokeColor : "#fff",
+      data : values,
+      mouseover: function(data) {
+        // data returns details about the point hovered, such as x and y position and index, as
+        // well as details about the hover event in data.event
+        // You can do whatever you like here, but here is a sample implementation of a tooltip
+        var active_value = values[data.point.dataPointIndex];
+        var active_date = labels[data.point.dataPointIndex];
+        // For details about where this tooltip came from, read below
+        tooltip.html(active_date + " - " + active_value).css("position", "absolute").css("left", data.point.x-17).css("top", data.point.y-55).css("display", 'block');
+      },
+      mouseout: function (data) {
+        // Hide the tooltip
+        tooltip.html("").css("display", "none");
+      }
+    }
+  ]
+};
+
+var ctx = document.getElementById("myCanvasElement").getContext("2d");
+var chart = new Chart(ctx).Line(data);
+```
+
+As you can see above, we can easily add an HTML tooltip to the data point by using the x and y position of the point hovered. Above, I offset the tooltip by a few pixels, position it absolutely, and format using plain old CSS/HTML. The absolute position works because I wrap my canvas in a relative div and put the tooltip as a sibling to the canvas:
+```html
+<div style="position: relative;">
+  <canvas id="myCanvasElement" width="400" height="400"></canvas>
+  <div id="tooltip"></div>
+</div>
+```
+
+Make your tooltips as fancy as you like now! My implementation:
+![Sample Chart.js Tooltip](http://github.com/jhdavids8/Chart.js/raw/master/sample_tooltip.png)
 
 Documentation
 -------