Add delegate readme

@@ -31,7 +31,6 @@ You will need LLVM 3.0 or later in order to build PNChart.
 
 ### Copy the PNChart folder to your project
 
-#### Line Chart
 
 [![](https://dl.dropboxusercontent.com/u/1599662/line.png)](https://dl.dropboxusercontent.com/u/1599662/line.png)
 
@@ -76,6 +75,45 @@ You will need LLVM 3.0 or later in order to build PNChart.
 
 ```
 
+#### Callback
+
+```objective-c
+  #import "PNChart.h"
+
+//For LineChart
+
+PNChart * lineChart = [[PNChart alloc] initWithFrame:CGRectMake(0, 135.0, SCREEN_WIDTH, 200.0)];
+lineChart.backgroundColor = [UIColor clearColor];
+[lineChart setXLabels:@[@"SEP 1",@"SEP 2",@"SEP 3",@"SEP 4",@"SEP 5",@"SEP 6",@"SEP 7"]];
+[lineChart setYValues:@[@1,@24,@12,@18,@30,@10,@21]];
+[lineChart strokeChart];
+
+lineChart.delegate = self;
+
+[viewController.view addSubview:lineChartLabel];
+[viewController.view addSubview:lineChart];
+
+viewController.title = @"Line Chart";
+
+```
+
+```objective-c
+  #import "PNChart.h"
+
+  //For DelegateMethod
+
+
+-(void)userClickedOnLineKeyPoint:(CGPoint)point andPointIndex:(NSInteger)index{
+    NSLog(@"Click Key on line %f, %f and index is %d",point.x, point.y,index);
+}
+
+-(void)userClickedOnLinePoint:(CGPoint)point {
+    NSLog(@"Click on line %f, %f",point.x, point.y);
+}
+
+```
+
+
 ## License
 
 This code is distributed under the terms and conditions of the [MIT license](LICENSE).