We don't have a canned one. Never thought about doing that and I'm not sure Facebook would accept it.
With that said, you can take a video with your own cellphone of you clicking on your computer. It doesn't have to be long, edited or pretty in any way. Simply show either the post ability or the stream showing functionality (depending on what you use) and how a user would access it.
Also, please note that you don't need to submit your app for review if just you, the Facebook admin, is using that feature. The only time you need to go through review is if you'll be requesting those permissions from regular users to post to a page or something, which isn't usually the common case.
I hope that helps explain,
Alex