Don't be so explicit with worktree creation

Makefile

@@ -15,7 +15,7 @@ all : $(OUT_MARKUP) $(OUT_OTHERS)
 
 prepare : $(OUT)
 	git fetch origin public
-	git worktree add --track -B public $(OUT) origin/public
+	git worktree add $(OUT) public
 
 wipe :
 	find $(OUT) -mindepth 1 -not -name '.git' -delete