Add Authorization documentation

Author: toastercup

README.md

@@ -22,13 +22,17 @@ Alternatively, cortex-client will handle OAuth2 authentication for you:
 ```ruby
 require 'cortex-client'
 
-client = Cortex::Client.new(key: 'my-app-id', secret: 'secrey-key-ssh', base_url: 'base_url', scopes: 'view:posts view:media')
+client = Cortex::Client.new(key: 'my-app-id', secret: 'my-app-secret', base_url: 'base_url', scopes: 'view:posts view:media')
 
  client.posts.query().each do |post|
   puts post
  end
 ```
 
+## Authorization
+
+For more information about `scopes` and how to obtain an application `key` and `secret`, check [Cortex's authorization documentation](https://github.com/cbdr/cortex#authorization).
+
 ## Result object
 
 Cortex::Client will return a Cortex::Result object. The following methods are available: