document --index-version for index-pack and pack-objects

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-index-pack.txt

@@ -68,6 +68,11 @@ OPTIONS
 	message can later be searched for within all .keep files to
 	locate any which have outlived their usefulness.
 
+--index-version=<version>[,<offset>]::
+	This is intended to be used by the test suite only. It allows
+	to force the version for the generated pack index, and to force
+	64-bit index entries on objects located above the given offset.
+
 
 Note
 ----

Documentation/git-pack-objects.txt

@@ -138,6 +138,11 @@ base-name::
 	length, this option typically shrinks the resulting
 	packfile by 3-5 per-cent.
 
+--index-version=<version>[,<offset>]::
+	This is intended to be used by the test suite only. It allows
+	to force the version for the generated pack index, and to force
+	64-bit index entries on objects located above the given offset.
+
 
 Author
 ------