chang to more clearly sentence

Author: 狄卢

book/03-git-branching/sections/rebasing.asc

@@ -79,7 +79,7 @@ You can take the changes on client that aren't on server (`C8` and `C9`) and rep
 $ git rebase --onto master server client
 ----
 
-This basically says, ``Check out the client branch, figure out the patches from the common ancestor of the `client` and `server` branches, and then replay them onto `master`.''
+This basically says, ``Take the `client` branch, figure out the patches since it diverged from the `master` branch, and replay these patches in the `client` branch as if it was based directly off the `master` branch instead.''
 It's a bit complex, but the result is pretty cool.
 
 .Rebasing a topic branch off another topic branch