Updated README.

README.md

@@ -1,8 +1,8 @@
 # Errawr::Rails
 
-Errawr support for Rails
+Raise and render errors in Rails using Errawr
 
-[![Build Status](https://travis-ci.org/anthonator/errawr-rails.png?branch=master)](https://travis-ci.org/anthonator/errawr-rails) [![Coverage Status](https://coveralls.io/repos/anthonator/errawr-rails/badge.png?branch=master)](https://coveralls.io/r/anthonator/errawr-rails?branch=master)
+[![Build Status](https://travis-ci.org/anthonator/errawr-rails.png?branch=master)](https://travis-ci.org/anthonator/errawr-rails) [![Coverage Status](https://coveralls.io/repos/anthonator/errawr-rails/badge.png?branch=master)](https://coveralls.io/r/anthonator/errawr-rails?branch=master) [![Code Climate](https://codeclimate.com/github/anthonator/errawr-rails.png)](https://codeclimate.com/github/anthonator/errawr-rails)
 
 ## Installation
 
@@ -20,7 +20,109 @@ Or install it yourself as:
 
 ## Usage
 
-TODO: Write usage instructions here
+### Getting Started
+
+To start raising errors in Rails just include ```Errawr::Rails``` in a controller. This will provide access to the ```#error!``` method in your controller.
+
+```ruby
+class SomeController < ApplicationController
+  include Errawr::Rails
+
+  def index
+    if params[:dont_work] == true
+      error!(:bad_request)
+    end
+  end
+end
+```
+
+### Rendering Error Responses
+
+If you'd like to catch and render errors in a particular format include ```Errawr::Rails``` using the ```#with_renderer``` method.
+
+```ruby
+class SomeController < ApplicationController
+  include Errawr::Rails.with_renderer(Rails::Errawr::Renderers::JSON)
+
+  def index
+    if params[:dont_work] == true
+      error!(:bad_request)
+    end
+  end
+end
+```
+
+The above example will render the error as JSON using the following format:
+
+```json
+{
+  "error": "bad_request",
+  "description": "Bad Request"
+}
+```
+
+Depending on what renderer is used additional metadata may be added to the response output:
+
+```ruby
+class SomeController < ApplicationController
+  include Errawr::Rails.with_renderer(Rails::Errawr::Renderers::JSON)
+
+  def index
+    if params[:dont_work] == true
+      error!(:bad_request, metadata: { extra_info: 'I like candy' })
+    end
+  end
+end
+```
+
+```json
+{
+  "error": "bad_request",
+  "description": "Bad Request",
+  "extra_info": "I like candy"
+}
+```
+
+Currently the only renderer that ships with Errawr::Rails is ```Rails::Errawr::Renderers::JSON```.
+
+
+### Custom Renderers
+
+To create a custom renderer simple create a class with that specifies a ```call``` method that accepts a single parameter. The method can return anything that the Rails ```render``` method will accept.
+
+```ruby
+class MyCustomRenderer
+  def call(error)
+  {
+    json: {
+      hello: 'world'
+    }
+  }
+  end
+end
+```
+
+```ruby
+class SomeController < ApplicationController
+  include Errawr::Rails.with_renderer(MyCustomRenderer)
+
+  def index
+    if params[:dont_work] == true
+      error!(:bad_request)
+    end
+  end
+end
+```
+
+```json
+{
+  "hello": "world"
+}
+```
+
+### HTTP Status Codes
+
+Errawr::Rails uses the [Errawr::HTTP](https://github.com/anthonator/errawr-http) gem to add support for [4xx](https://github.com/anthonator/errawr-http#supported-4xx-status-codes) and [5xx](https://github.com/anthonator/errawr-http#supported-5xx-status-codes) HTTP status code errors.
 
 ## Contributing