Da un accordo tra vari motori di ricerca si è convenuto un sistema più semplice e rapido per gli utenti per segnalare i Sitemap dei propri siti web. D'ora in poi, infatti, non sarà più necessario segnalare manualmente il proprio file ai singoli motori, ma sarà sufficiente segnalarne il percorso sul file robots.txt.
Eccovi la procedura estratta dal blog di google:

...it's now easier for you to tell us where your Sitemaps live. We wondered if we could make it so easy that you wouldn't even have to tell us and every other search engine that supports Sitemaps. But howà Well, every website can have a robots.txt file in a standard location, so we decided to let you tell us about your Sitemap in the robots.txt file. All you have to do is add a line like

Sitemap: http://www.mysite.com/sitemap.xml

to your robots.txt file. Just make sure you include the full URL, including the http://. That's it. Of course, we still think it's useful to submit your Sitemap through Webmaster tools so you can make sure that the Sitemap was processed without any issues and you can get additional statistics about your site...