Interval.md

-Reads Postgresql's interval data type and transforms it into Rails' `ActiveSupport::Duration`. [PostgreSQL Docs](https://www.postgresql.org/docs/9.4/static/datatype-datetime.html#DATATYPE-INTERVAL-INPUT)
+Reads PostgreSQL's interval data type and transforms it into Rails' `ActiveSupport::Duration`. [PostgreSQL Docs](https://www.postgresql.org/docs/9.4/static/datatype-datetime.html#DATATYPE-INTERVAL-INPUT)
 
 # How it works
 
 ### Migration
 
+Just set the type of the column as `interval` when creating a table.
+```ruby
+create_table "courses" do |t|
+  t.string   "title",    null: false
+  t.interval "duration"
+end
+```
 
+Or when you are adding or column, just use `:interval` as type.
+```ruby
+add_column :courses, :duration, :interval
+```
 
 ### Using it
 
+The column is automatically identified and the value is turn into `ActiveSupport::Duration`. So any of the methods available on it can be used direct from your field. [RubyOnRails Doc](http://api.rubyonrails.org/classes/ActiveSupport/Duration.html)
+```ruby
+# Shows when you'll be finishing the course
+course.duration.from_now
+```
\ No newline at end of file