Add usage not to README
Add usage not to README

fphilipe/premailer-rails,doorkeeper/premailer-rails,controlshift/premailer-rails,controlshift/premailer-rails,uswitch/premailer-rails,doorkeeper/premailer-rails,fphilipe/premailer-rails,controlshift/premailer-rails,uswitch/premailer-rails,fphilipe/premailer-rails