Add some info about -f to the "expects two arguments" error.

Ping #1722

command/write.go

@@ -33,7 +33,7 @@ func (c *WriteCommand) Run(args []string) int {
 
 	args = flags.Args()
 	if len(args) < 2 && !force {
-		c.Ui.Error("write expects at least two arguments")
+		c.Ui.Error("write expects at least two arguments; use -f to perform the write anyways")
 		flags.Usage()
 		return 1
 	}