There are many ways that can be used to submit sitemap to search engines.

Lets discuss approaches

1. Put sitemap.xml in public folder and you are done.
    Crawlers will find it through url
    http://yourdomain.com/sitemap.xml

2. There are many online sites which generates sitemaps for you.
    like http://www.xml-sitemaps.com/

3. Open following urls in browser. Be sure to add xml sitemap path for your site.

a. Google submit
    http://www.google.com/webmasters/tools/ping?sitemap=XML_SITEMAP_PATH

b. Yahoo Submit
    http://search.yahooapis.com/SiteExplorerService/V1/ping?sitemap=XML_SITEMAP_PATH

c. Ask Submit
    http://submissions.ask.com/ping?sitemap=XML_SITEMAP_PATH

d. Webmaster submit
    http://webmaster.live.com/ping.aspx?siteMap=XML_SITEMAP_PATH

5. Best practices in rails to submit sitemap is scheduled task (cron job).
    Write a rake task that will generate sitemap in rails public folder and
    will submit sitemap.xml file to search engines. ( as mentioned above.)

Got easy :)