Documentation: git-filter-branch honors replacement refs

Make it clear that git-filter-branch will honor and make permanent
replacement refs as well as grafts.

Signed-off-by: Peter Collingbourne <peter@pcc.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-filter-branch.txt

@@ -32,8 +32,9 @@ changes, which would normally have no effect.  Nevertheless, this may be
 useful in the future for compensating for some git bugs or such,
 therefore such a usage is permitted.
 
-*NOTE*: This command honors `.git/info/grafts`. If you have any grafts
+*NOTE*: This command honors `.git/info/grafts` and `.git/refs/replace/`.
-defined, running this command will make them permanent.
+If you have any grafts or replacement refs defined, running this command
+will make them permanent.
 
 *WARNING*! The rewritten history will have different object names for all
 the objects and will not converge with the original branch.  You will not