update doc

Author: ben-lin

Readme.md

@@ -192,6 +192,28 @@ Set an end point for a group of parallel tasks.
 
 
 
+### flow.error( callback );
+
+Error handler for in case there is any.
+
+#### Arguments
+
+> callback
+
+    type: Function
+    desc: Error handler to break the flow.
+
+#### Example code
+
+    var Flow = require( 'node.flow' );
+    var flow = new Flow();
+
+    flow.error( function ( err ){
+      console.log( err );
+    });
+
+
+
 ### flow.end( callback, arg1, arg2, ... );
 
 Call the tasks one after another in the stack.
@@ -343,4 +365,4 @@ MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
-SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.