Document the "ignore objects" feature of git-pack-redundant

Signed-off-by: NLukas Sandström <lukass@etek.chalmers.se>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

Documentation/git-pack-redundant.txt

@@ -16,6 +16,14 @@ This program computes which packs in your repository
 are redundant. The output is suitable for piping to
 'xargs rm' if you are in the root of the repository.
 
+git-pack-redundant accepts a list of objects on standard input. Any objects
+given will be ignored when checking which packs are required. This makes the 
+following command useful when wanting to remove packs which contain unreachable
+objects.
+
+git-fsck-objects --full --unreachable | cut -d ' ' -f3 | \
+git-pack-redundant --all | xargs rm
+
 OPTIONS
 -------