See here for details: https://developers.google.com/webmaster-tools/v3/sitemaps/submit
add_sitemap(siteURL, feedpath)
The URL of the website to delete. Must include protocol (http://).
The URL of the sitemap to submit. Must include protocol (http://).
TRUE if successful, raises an error if not.
Other sitemap admin functions: delete_sitemap
,
list_sitemaps