README.md in gdatastore_mapper-0.1.4 vs README.md in gdatastore_mapper-0.1.5

@@ -1,6 +1,7 @@
 # GdatastoreMapper
+[![CircleCI](https://circleci.com/gh/shinyaK14/gdatastore_mapper/tree/master.svg?style=svg)](https://circleci.com/gh/shinyaK14/gdatastore_mapper/tree/master)  [![Gem Version](https://badge.fury.io/rb/gdatastore_mapper.svg)](https://badge.fury.io/rb/gdatastore_mapper)
 
 GdatastoreMapper is a mapper framework for Google Cloud Datastore in Ruby / Ruby on Rails.
 Once you install GdatastoreMapper you can use Google Cloud Datastore like ActiveRecord.
 
 ## Table of Contents
@@ -12,10 +13,12 @@
 - [Persistence Methods](#persistence-methods)
 - [Scoping Methods](#scoping-methods)
 - [Timestamp](#timestamp)
 - [Associations](#associations)
   - [One to Many](#one-to-many)
+- [Callbacks](#callbacks)
+- [Contact](#contact)
 - [Development](#development)
 
 ## Demo
 
 Here is [demo](https://gdatastore-mapper-sample.appspot.com/). The demo works with Google Cloud Datastore.
@@ -150,10 +153,11 @@
 All records have created_at and updated_at. They will be updated automatically.
 
 ## Associations
 
 ### One to Many
+Associations can be set the same as Active Record.
 
 example of one to many relationship
 
 ```ruby
 class Book
@@ -194,9 +198,30 @@
 ```
 ```
 harry_poter.author
 => [#<Author:0x00 @name="J. K. Rowling" .... ]
 ```
+
+## Callbacks
+
+```ruby
+class Book
+  include GdatastoreMapper::Base
+
+  before_save :something_before_save
+
+  private
+  def something_before_save
+    something that you want
+  end
+
+end
+```
+
+## Contact
+
+Please shoot me an e-mail if you find any issues, ideas and comments. [e-mail]
+Thanks!
 
 ## Development
 
 After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.