docs: clarify security-bugs disclosure policy

I think we need to soften the language a bit.  It might scare folks
off, especially the:

	 We prefer to fully disclose the bug as soon as possible.

which is not really the case.  Linus says:

	It's not full disclosure, it's not coordinated disclosure,
	and it's not "no disclosure".  It's more like just "timely
	open fixes".

I changed a bit of the wording in here, but mostly to remove the word
"disclosure" since it seems to mean very specific things to people
that we do not mean here.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>