SubmittingPatches: add section about AI

SubmittingPatches: add section about AI

As more and more developer tools use AI, we are facing two main risks
related to AI generated content:

  - its situation regarding copyright and license is not clear,
    and:

  - more and more bad quality content could be submitted for review to
    the mailing list.

To mitigate both risks, let's add an "Use of Artificial Intelligence"
section to "Documentation/SubmittingPatches" with the goal of
discouraging its blind use to generate content that is submitted to
the project, while still allowing us to benefit from its help in some
innovative, useful and less risky ways.

Helped-by: Rick Sanders <rick@sfconservancy.org>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>