docs: security-bugs: clarify some mandatory steps for AI reports

docs: security-bugs: clarify some mandatory steps for AI reports

The security team is still seeing a lot of reports lacking a full patch
and showing missing contents and formatting issues. Since AI assistants
tend to be better than humans at following instructions, let's defer to
coding-assistants.rst to follow mandatory steps, and insist on the plain
text format, as well as asking for recipient addresses and an e-mail
client setup hint to be mentioned early in the report for the reporter.

Also add a link to https://github.com/masoncl/kres.git which contains
way more advanced and detailed steps for those willing to go further.

Tested with Opus-5 and Qwen3.6-27B-Architect-Polaris2-Fable-B-F451, both
of which proceeded according to instructions.

Cc: Greg KH <greg@kroah.com>
Cc: Chris Mason <clm@meta.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Link: https://patch.msgid.link/20260802203540.3453-6-w@1wt.eu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>