slightly better auto gc message

Signed-off-by: NNicolas Pitre <nico@cam.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin-gc.c

@@ -205,7 +205,7 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 		prune = 0;
 		if (!need_to_gc())
 			return 0;
-		fprintf(stderr, "Packing your repository for optimum "
+		fprintf(stderr, "Auto packing your repository for optimum "
 			"performance. You may also\n"
 			"run \"git gc\" manually. See "
 			"\"git help gc\" for more information.\n");