Once upon a time, the world was run by rich men.   And all was good.   But then the world was conquered by other rich men.   And that is something the first group of rich men could not allow.   That is the reason behind Netflix’s new film “Inside Bill’s Brain: Decoding Bill Gates.”   The three-part documentary goes live on Sept. 20. But the film’s aims are clear from the trailer.   It’s a vanity project about…