revision.c: explain what tree_difference does

diff --git a/Documentation/git-diff-tree.txt b/Documentation/git-diff-tree.txt
index f7e8ff2968d6c443220ea9e9667255ebdd29b602..5d6e9dc751aef6e30582b399ae09f81c043e6de1 100644 (file)
--- a/Documentation/git-diff-tree.txt
+++ b/Documentation/git-diff-tree.txt
@@ -73,10 +73,7 @@ separated with a single space are given.
        This flag causes "git-diff-tree --stdin" to also show
        the commit message before the differences.
 
---pretty[=(raw|medium|short)]::
-       This is used to control "pretty printing" format of the
-       commit message.  Without "=<style>", it defaults to
-       medium.
+include::pretty-formats.txt[]
 
 --no-commit-id::
        git-diff-tree outputs a line with the commit ID when