Update readme on retroactive cleaning
Update readme on retroactive cleaning

lpsinger/git-fat,PersonifyInc/git-fat,ajohnson23/git-fat,cnweibo/git-fat,jedbrown/git-fat,ciena-blueplanet/git-fat,wikimedia/git-fat,lpsinger/git-fat,ciena-blueplanet/git-fat,cyaninc/git-fat,grahamgilbert/git-fat,wikimedia/operations-debs-git-fat,PersonifyInc/git-fat,cnweibo/git-fat,ajohnson23/git-fat,wikimedia/operations-debs-git-fat,michaelcontento/git-fat,michaelcontento/git-fat,grahamgilbert/git-fat,jedbrown/git-fat,cyaninc/git-fat,wikimedia/git-fat