Add update data part.

README.md

@@ -175,3 +175,17 @@ song2.setDuration(356);
 song2.setAlbum(album);
 song2.save();
 ```
+
+#### 3. Update data
+Each model which inherits from **DataSupport** would also have **update()** and **updateAll()** method. You can update a single record by a specified id:
+``` java
+Album albumToUpdate = new Album();
+albumToUpdate.setPrice(20.99f); // raise the price
+albumToUpdate.update(id);
+```
+Or you can update multiple records by a where condition:
+``` java
+Album albumToUpdate = new Album();
+albumToUpdate.setPrice(20.99f); // raise the price
+albumToUpdate.updateAll("name = ?", "album");
+```