Merge branch 'zh/commit-trailer'

"git commit" learned "--trailer <key>[=<value>]" option; together
with the interpret-trailers command, this will make it easier to
support custom trailers.

* zh/commit-trailer:
  commit: add --trailer option

Documentation/git-commit.txt

@@ -14,7 +14,8 @@ SYNOPSIS
 	   [--allow-empty-message] [--no-verify] [-e] [--author=<author>]
 	   [--date=<date>] [--cleanup=<mode>] [--[no-]status]
 	   [-i | -o] [--pathspec-from-file=<file> [--pathspec-file-nul]]
-	   [-S[<keyid>]] [--] [<pathspec>...]
+	   [(--trailer <token>[(=|:)<value>])...] [-S[<keyid>]]
+	   [--] [<pathspec>...]
 
 DESCRIPTION
 -----------
@@ -199,6 +200,17 @@ The `-m` option is mutually exclusive with `-c`, `-C`, and `-F`.
 
 include::signoff-option.txt[]
 
+--trailer <token>[(=|:)<value>]::
+	Specify a (<token>, <value>) pair that should be applied as a
+	trailer. (e.g. `git commit --trailer "Signed-off-by:C O Mitter \
+	<committer@example.com>" --trailer "Helped-by:C O Mitter \
+	<committer@example.com>"` will add the "Signed-off-by" trailer
+	and the "Helped-by" trailer to the commit message.)
+	The `trailer.*` configuration variables
+	(linkgit:git-interpret-trailers[1]) can be used to define if
+	a duplicated trailer is omitted, where in the run of trailers
+	each trailer would appear, and other details.
+
 -n::
 --no-verify::
 	This option bypasses the pre-commit and commit-msg hooks.