title: Unison: sync only in one direction
body: <p>If I have folder A and B, is it possible to sync the new files from A to B and to not erase in B files erased in A?</p>
  
  <p>That is to say, I would like to use B as a big container for any file, including the one that I once synchronized from A and than erased. I think is considered kind of "one way syncing".</p>