Readme update

Author: Kyle d'Oliveira

README.md

@@ -1,6 +1,35 @@
 # PolymorphicIntegerType
 
-TODO: Write a gem description
+Rails' polymorphic assocaitions are pretty useful. The example they give to set it up looks like:
+```ruby
+class Picture < ActiveRecord::Base
+  belongs_to :imageable, polymorphic: true
+end
+ 
+class Employee < ActiveRecord::Base
+  has_many :pictures, as: :imageable
+end
+ 
+class Product < ActiveRecord::Base
+  has_many :pictures, as: :imageable
+end
+```
+
+With a migration that looks like:
+```ruby
+class CreatePictures < ActiveRecord::Migration
+  def change
+    create_table :pictures do |t|
+      t.string  :name
+      t.integer :imageable_id
+      t.string  :imageable_type
+      t.timestamps
+    end
+  end
+end
+```
+
+The problem with this approach is the `imageable_type` is a string (and by default it is 255 characters). This is a little rediculous. For comparison, if we had a state machine with X states, would be describe the states with strings `"State1", "State2", etc` or would be just enumerate the state column and make it an integer. This gem will make it so we can use an integer for the `imageable_type` column. 
 
 ## Installation
 
@@ -18,7 +47,86 @@ Or install it yourself as:
 
 ## Usage
 
-TODO: Write usage instructions here
+The gem is pretty straightforward to use.
+
+First, include the extensions module and add the `integer_type`  option to the assocaitions that are going to be using this. (That way it will play nicely with polymorphic association you would rather the type remain as a string)
+```ruby
+class Picture < ActiveRecord::Base
+  include PolymorphicIntegerType::Extensions
+  belongs_to :imageable, polymorphic: true, :integer_type => true
+end
+ 
+class Employee < ActiveRecord::Base
+  include PolymorphicIntegerType::Extensions
+  has_many :pictures, as: :imageable, :integer_type => true
+end
+ 
+class Product < ActiveRecord::Base
+  include PolymorphicIntegerType::Extensions
+  has_many :pictures, as: :imageable, :integer_type => true
+end
+```
+
+Second, you need to create a mapping for the polymorphic associations. This should be loaded before the models. Putting it in an initializer is good (`config/initializers/polymorphic_type_mapping.rb`)
+```ruby
+PolymorphicIntegerType::Mapping.configuration do |config|
+
+  config.add :imageable, {1 => "Employee", 2 => "Product" }  	
+
+end 
+```
+
+Note: The mapping here can start from whatever integer you wish, but I would advise not to use 0. The reason being that if you had a new class, for instance `Avatar`, and also wanted to use this polymorphic association but forgot to include it in the mapping, it would effectively get `to_i` called on it and stored in the database. `"Avatar".to_i == 0` so if your mapping included 0, this would create a weird bug. 
+
+If you want to migrate from a polymorphic association that is already a string you'll need to setup a migration (assuming sql for the time being. But this should be pretty straightforward)
+```ruby
+class PictureToPolymorphicIntegerType < ActiveRecord::Migration
+  
+  def up
+    execute <<-SQL
+      ALTER TABLE pictures
+      ADD COLUMN new_imageable_type INTEGER
+    SQL
+
+    execute <<-SQL
+      UPDATE reminders
+      SET new_imageable_type = CASE imageable_type
+                               WHEN 'Employee' THEN 1
+                               WHEN 'Product' THEN 2
+                             END
+    SQL
+    execute <<-SQL
+      ALTER TABLE pictures
+      DROP COLUMN imageable_type,
+      CHANGE COLUMN new_imageable_type imageable_type INTEGER
+    SQL
+  end
+
+  def down
+    execute <<-SQL
+      ALTER TABLE pictures
+      ADD COLUMN new_imageable_type VARCHAR(255)
+    SQL
+
+    execute <<-SQL
+      UPDATE picture
+      SET new_imageable_type = CASE imageable_type
+                               WHEN 1 THEN 'Employee'
+                               WHEN 2 THEN 'Product'
+                             END
+    SQL
+    execute <<-SQL
+      ALTER TABLE picture
+      DROP COLUMN imageable_type,
+      CHANGE COLUMN new_imageable_type imageable_type VARCHAR(255)
+    SQL
+  end
+end
+```
+
+Lastly, you will need to be careful of any place where you are doing raw sql queries with the string (`imageable_type = 'Employee'`). They should use the integer instead
+  
+
 
 ## Contributing