docs: remove some index.rst cruft

There is some useless boilerplate text that was added by sphinx when this
file was first created; take it out.

Reviewed-by: David Vernet <void@manifault.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20220927160559.97154-5-corbet@lwn.net


Signed-off-by: Jonathan Corbet <corbet@lwn.net>