Merge branch 'ab/gc-doc-update'

The documentation of "git gc" has been updated to mention that it
is no longer limited to "pruning away crufts" but also updates
ancillary files like commit-graph as a part of repository
optimization.

* ab/gc-doc-update:
  gc doc: mention the commit-graph in the intro

Author: gitster

Documentation/git-gc.txt

@@ -17,7 +17,8 @@ Runs a number of housekeeping tasks within the current repository,
 such as compressing file revisions (to reduce disk space and increase
 performance), removing unreachable objects which may have been
 created from prior invocations of 'git add', packing refs, pruning
-reflog, rerere metadata or stale working trees.
+reflog, rerere metadata or stale working trees. May also update ancillary
+indexes such as the commit-graph.
 
 Users are encouraged to run this task on a regular basis within
 each repository to maintain good disk space utilization and good