doc:it: alignement clarification about sign-off and Co-developed-by

Align Italian documentation after the following patch to the main documents

commit 24a2bb90 docs: Clarify the usage and sign-off requirements for Co-developed-by

Signed-off-by: Federico Vaga <federico.vaga@vaga.pv.it>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>