Mention options for schema in sitemap

Add clear way to change schema in `sitemap.xml` to https on `sitemap`
documentation page

CONTRIBUTORS.rst

@@ -435,6 +435,7 @@ Contributors
 * Storm Heg
 * Daniel (aritas1)
 * timmysmalls
+* dtwm
 
 Translators
 ===========

docs/reference/contrib/sitemaps.rst

@@ -88,6 +88,7 @@ a valid, crawlable hostname. If you change the site's hostname from
     </url>
 
 
+If you change the site's port to ``443``, the ``https`` scheme will be used.
 Find out more about :ref:`working with Sites<site-model-ref>`.