Sitemaps are now autodiscovered by major search engines

Ever since Yahoo joined forces with Google and Microsoft in creating, they have been pondering a way to autodetect sitemaps without having the webcrawlers crawl everywhere to find it.
Now they’ve come up with a brilliant solution. Add to you robots.txt file:
Where is your URL. This way, all search engines are using a universal standard and will be able to crawl more efficiently and update your sites in the search engines more quickly.
Via YahooSearch