contrib/subtree: fix synopsis

Fix the documentation of add to show that a repository can be
specified along with a commit.

Suggested by Yann Dirson <dirson@bertin.fr>.

Signed-off-by: David A. Greene <greened@obbligato.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/subtree/git-subtree.sh

@@ -9,6 +9,7 @@ if [ $# -eq 0 ]; then
 fi
 OPTS_SPEC="\
 git subtree add   --prefix=<prefix> <commit>
+git subtree add   --prefix=<prefix> <repository> <commit>
 git subtree merge --prefix=<prefix> <commit>
 git subtree pull  --prefix=<prefix> <repository> <refspec...>
 git subtree push  --prefix=<prefix> <repository> <refspec...>
@@ -502,6 +503,11 @@ cmd_add()
 
 	    "cmd_add_commit" "$@"
 	elif [ $# -eq 2 ]; then
+	    # Technically we could accept a refspec here but we're
+	    # just going to turn around and add FETCH_HEAD under the
+	    # specified directory.  Allowing a refspec might be
+	    # misleading because we won't do anything with any other
+	    # branches fetched via the refspec.
 	    git rev-parse -q --verify "$2^{commit}" >/dev/null ||
 	    die "'$2' does not refer to a commit"
 

contrib/subtree/git-subtree.txt

@@ -9,7 +9,8 @@ git-subtree - Merge subtrees together and split repository into subtrees
 SYNOPSIS
 --------
 [verse]
-'git subtree' add   -P <prefix> <commit>
+'git subtree' add   -P <prefix> <refspec>
+'git subtree' add   -P <prefix> <repository> <refspec>
 'git subtree' pull  -P <prefix> <repository> <refspec...>
 'git subtree' push  -P <prefix> <repository> <refspec...>
 'git subtree' merge -P <prefix> <commit>