doc: give some guidelines for error messages

diff --git a/Documentation/git-commit-tree.txt b/Documentation/git-commit-tree.txt
index cafdc9642d312776b0122c4d010a9e9246bad8ff..a469eab06683dece65f447a6c2691c30fe54b214 100644 (file)
--- a/Documentation/git-commit-tree.txt
+++ b/Documentation/git-commit-tree.txt
@@ -55,8 +55,13 @@ OPTIONS
        from the standard input.
 
 -S[<keyid>]::
+--gpg-sign[=<keyid>]::
        GPG-sign commit.
 
+--no-gpg-sign::
+       Countermand `commit.gpgsign` configuration variable that is
+       set to force each and every commit to be signed.
+
 
 Commit Information
 ------------------