README.md in rubocop-performance-1.19.1 vs README.md in rubocop-performance-1.20.0

@@ -51,9 +51,11 @@
 ```
 
 ### Rake task
 
 ```ruby
+require 'rubocop/rake_task'
+
 RuboCop::RakeTask.new do |task|
   task.requires << 'rubocop-performance'
 end
 ```