Changed a sentence about Git project

A sentence about the git project seemed confusing to those who were
not familiar with it. So changed it to make it more easily
understandable.

Author: Kaartic Sivaraam

book/05-distributed-git/sections/maintaining.asc

@@ -346,7 +346,8 @@ If they're safe, they're merged into `next`, and that branch is pushed up so eve
 image::images/large-merges-1.png[Managing a complex series of parallel contributed topic branches.]
 
 If the topics still need work, they're merged into `pu` instead.
-When it's determined that they're totally stable, the topics are re-merged into `master` and are then rebuilt from the topics that were in `next` but didn't yet graduate to `master`.
+When it's determined that they're totally stable, the topics are re-merged into `master`.
+The `next` and `pu` branches are then rebuilt from the `master`.
 This means `master` almost always moves forward, `next` is rebased occasionally, and `pu` is rebased even more often:
 
 .Merging contributed topic branches into long-term integration branches.