Document git-patch-id a bit better.

Pavel Roskin wondered what the SHA1 output at the beginning of
git-diff-tree was about.  The only consumer of that information
so far is this git-patch-id command, which was inadequately
documented.

Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/Documentation/git-patch-id.txt b/Documentation/git-patch-id.txt
index 3e560a37e835bb59f12754591c5c32bac671f57c..c8bd1977790b2611d4b7974fc3a716d99b888a74 100644 (file)
--- a/Documentation/git-patch-id.txt
+++ b/Documentation/git-patch-id.txt
@@ -18,6 +18,12 @@ ID" are almost guaranteed to be the same thing.
 
 IOW, you can use this thing to look for likely duplicate commits.
 
 
 IOW, you can use this thing to look for likely duplicate commits.
 

+When dealing with git-diff-tree output, it takes advantage of
+the fact that the patch is prefixed with the object name of the
+commit, and outputs two 40-byte hexadecimal string.  The first
+string is the patch ID, and the second string is the commit ID.
+This can be used to make a mapping from patch ID to commit ID.
+

 OPTIONS
 -------
 <patch>::
 OPTIONS
 -------
 <patch>::