README: Fix spelling/capitalization

- Fix spelling/capitalization s/Restructured/ReStructured/

Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240207122127.9182-1-thorsten.blum@toblux.com