improved docs

README.md

@@ -82,12 +82,17 @@ class User < ApplicationRecord
     model_description "A user of the system"
     property :name, description: "The user's name", title: "Full Name"
     property :group, enum: [1, 2, 3], default: 1, description: "The user's group"
+    virtual_property :age, type: "integer", description: "The user's age"
   end
 end
 ```
 
 In the example above, the `enhance_schema` method is used to add a description to the model, change the title of the `name` property and add a description. It adds an enum, default value and a description to the `group` property.
 
+Use the `property` keyword for the existing model attributes. In other words the symbol passed to the `property` method must be a column in the table that the model represents. Property does not accept a `type` argument, as the type is inferred from the column type.
+
+Use the `virtual_property` keyword for properties that are not columns in the table that the model represents.Virtual properties do accept a `type` argument, as the type cannot be inferred from the column type.
+
 
 ## Development