[PATCH 3/6] pack-protocol.txt: clarify 'obj-id' in the last ACK after 'done'

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

It's introduced in 1bd8c8f (git-upload-pack: Support the multi_ack
protocol - 2005-10-28) but probably better documented in the commit
message of 78affc4 (Add multi_ack_detailed capability to
fetch-pack/upload-pack - 2009-10-30)

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/technical/pack-protocol.txt | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Documentation/technical/pack-protocol.txt b/Documentation/technical/pack-protocol.txt
index c73b62f..eb0b8a1 100644
--- a/Documentation/technical/pack-protocol.txt
+++ b/Documentation/technical/pack-protocol.txt
@@ -338,7 +338,8 @@ during a prior round.  This helps to ensure that at least one common
 ancestor is found before we give up entirely.
 
 Once the 'done' line is read from the client, the server will either
-send a final 'ACK obj-id' or it will send a 'NAK'. The server only sends
+send a final 'ACK obj-id' or it will send a 'NAK'. 'obj-id' is the
+last SHA-1 determined to be common. The server only sends
 ACK after 'done' if there is at least one common base and multi_ack or
 multi_ack_detailed is enabled. The server always sends NAK after 'done'
 if there is no common base found.
-- 
1.8.5.2.240.g8478abd