scripts: Add placeholders for OPTIONS_SPEC

--text follows this line--
These commands currently lack OPTIONS_SPEC; allow people to
easily list with "git grep 'OPTIONS_SPEC=$'" what they can help
improving.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-commit.sh

@@ -5,6 +5,7 @@
 
 USAGE='[-a | --interactive] [-s] [-v] [--no-verify] [-m <message> | -F <logfile> | (-C|-c) <commit> | --amend] [-u] [-e] [--author <author>] [--template <file>] [[-i | -o] <path>...]'
 SUBDIRECTORY_OK=Yes
+OPTIONS_SPEC=
 . git-sh-setup
 require_work_tree