Documentation/security-bugs: Explain why plain text is preferred

The security contact list gets regular reports contained in archive
attachments. This tends to add some back-and-forth delay in dealing with
security reports since we have to ask for plain text, etc.

Signed-off-by: Kees Cook <[e-mail]>
Reviewed-by: Greg Kroah-Hartman <[e-mail]>
Acked-by: Jiri Kosina <[e-mail]>
Acked-by: Gustavo A. R. Silva <[e-mail]>
Acked-by: Will Deacon <[e-mail]>
Acked-by: Willy Tarreau <[e-mail]>
Link: https://lore.kernel.org/r/202007091110.205DC6A9@keescook
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/admin-guide/security-bugs.rst

···
 
 As it is with any bug, the more information provided the easier it
 will be to diagnose and fix.  Please review the procedure outlined in
-admin-guide/reporting-bugs.rst if you are unclear about what
+:doc:`reporting-bugs` if you are unclear about what
 information is helpful.  Any exploit code is very helpful and will not
 be released without consent from the reporter unless it has already been
 made public.
+
+Please send plain text emails without attachments where possible.
+It is much harder to have a context-quoted discussion about a complex
+issue if all the details are hidden away in attachments.  Think of it like a
+:doc:`regular patch submission <../process/submitting-patches>`
+(even if you don't have a patch yet): describe the problem and impact, list
+reproduction steps, and follow it with a proposed fix, all in plain text.
 
 Disclosure and embargoed information
 ------------------------------------