minor format change for the code sample in the readme

README.md

@@ -22,13 +22,15 @@ See the examples for detailed information on how to use maroon.
 
 Essentially you can define a context by using
 
+```ruby
 Context.define :context_name do
    role :role_name do
       print_self do |x| #notice no symbol
          p "#{role_name} #use role_name to refer to the role of said name
       end
    end
 end
+```
 
 ## Running Tests