Documentation: insist on the plain-text requirement for security reports

Documentation: insist on the plain-text requirement for security reports

As the trend of AI-generated reports is growing, the trend of unreadable
reports in gimmicky formats is following, and we cannot request that
developers rely on online viewers to be able to read a security report
full for formatting tags. Let's just insist on the plain text requirement
a bit more.

Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20251129141741.19046-1-w@1wt.eu>