X-UA-Compatible meta tag missing, sitemap, and robots.txt example

The X-UA-Compatible meta tag was missing from some HTML files.

robots.txt has an example for allowing all URLs to be crawled, but doesn't have an example for disallowing all URLs to be crawled.

An example sitemap was added. (Though I'm not sure if <loc>http://example.com/</loc> would fly with the Web Starter Kit guidelines.)
should be a separate PR