[PATCH] update-index doc: v4 is OK with JGit and libgit2

[Junio C Hamano <gitster@pobox.com>]

Being invented in late 2012 no longer makes the index v4 format
"relatively young".

The support for the index version 4 was added to libgit2 with their
5625d86b (index: support index v4, 2016-05-17) and to JGit with
their e9cb0a8e (DirCache: support index V4, 2020-08-10).

Let's update the paragraph that discouraged its use for folks overly
cautious about cross-tool compatibility.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 Documentation/git-update-index.txt | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/Documentation/git-update-index.txt b/Documentation/git-update-index.txt
index f4bb9c5daf..3d90d6f9ab 100644
--- a/Documentation/git-update-index.txt
+++ b/Documentation/git-update-index.txt
@@ -166,9 +166,12 @@ you will need to handle the situation manually.
 +
 Version 4 performs a simple pathname compression that reduces index
 size by 30%-50% on large repositories, which results in faster load
-time. Version 4 is relatively young (first released in 1.8.0 in
-October 2012). Other Git implementations such as JGit and libgit2
-may not support it yet.
+time. The first version to support it was Git 1.8.0 released in
+October 2012, and support for it was added to libgit2 in 2016 and
+JGit in 2020, respectively.  Older editions of this manual page called
+it "relatively young", but it should be considered mature technology
+these days.
+
 
 -z::
 	Only meaningful with `--stdin` or `--index-info`; paths are
-- 
2.42.0-rc2-7-gf9972720e9