Fix --models option description to match README (#649)

Author: rnitta

lib/annotate/parser.rb

@@ -123,7 +123,7 @@ def add_options_to_parser(option_parser) # rubocop:disable Metrics/MethodLength
         env['routes'] = 'true'
       end
 
-      option_parser.on('--models', "Annotate routes.rb with the output of 'rake routes'") do
+      option_parser.on('--models', "Annotate ActiveRecord models") do
         env['models'] = 'true'
       end