The doc page here: https://docs.mongodb.com/manual/reference/command/flushRouterConfig/ (basically the same in 3.2 also) doesn't show how the command is invoked. It needs to be called as:
> db.adminCommand("flushRouterConfig")

but that's not at all obvious from the documentation page. We should probably make sure we show an invocation of every command on it's documentation page.