Update sitemap to not use a page title (#4153)

Co-authored-by: Sang Ik Lee <sang.ik.lee@intel.com>
Co-authored-by: Scott Cyphers <diyessi@users.noreply.github.com>

doc/sphinx/source/sitemap.rst

 :orphan:
 
-Sitemap
-#######
-
 * :ref:`Getting Started <introduction>`
 
   .. toctree::