Update READMECustomize example
Update READMECustomize example

2 changes on it:
1. `Task.new` needs to receive the Rails.application
2. Need to clear the tasks generated before, otherwise it will run the old and the new ones.
zBMNForks/sprockets-rails,jordan-brough/sprockets-rails,jeremy/sprockets-rails,rails/sprockets-rails,Andreis13/sprockets-rails,maclover7/sprockets-rails,github/sprockets-rails,eileencodes/sprockets-rails,spodlecki/sprockets-rails,prathamesh-sonpatki/sprockets-rails,envato/sprockets-rails