Document commit.template configuration variable.

Add it to the list in config.txt and explicitly say that the
--template option to git-commit overrides the configuration variable.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -393,6 +393,9 @@ color.status.<slot>::
 	or `untracked` (files which are not tracked by git). The values of
 	these variables may be specified as in color.branch.<slot>.
 
+commit.template::
+	Specify a file to use as the template for new commit messages.
+
 diff.renameLimit::
 	The number of files to consider when performing the copy/rename
 	detection; equivalent to the git diff option '-l'.

Documentation/git-commit.txt

@@ -78,9 +78,8 @@ OPTIONS
 	Use the contents of the given file as the initial version
 	of the commit message. The editor is invoked and you can
 	make subsequent changes. If a message is specified using
-	the `-m` or `-F` options, this option has no effect. The
-	template file may also be specified using the `commit.template`
-	configuration variable.
+	the `-m` or `-F` options, this option has no effect. This
+	overrides the `commit.template` configuration variable.
 
 -s|--signoff::
 	Add Signed-off-by line at the end of the commit message.