docs: kernel-dev: faq: update tip on how to not include kernel in image

Since commit f6d963fa6d0e ("kernel: make kernel-base recommend
kernel-image, not depend"), present in Kirkstone 4.0, one should
set RRECOMMENDS and not RDEPENDS to avoid including the kernel in the
image, so let's update the documentation to reflect that.

Reported-by: Konstantin Kletschke <konstantin.kletschke@inside-m2m.de>
Cc: Quentin Schulz <foss+yocto@0leil.net>
(From yocto-docs rev: 7806a5d7ee986b92d4b8e438b14c18759e4421e5)

Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/kernel-dev/faq.rst

@@ -36,7 +36,7 @@ How do I install/not-install the kernel image on the root filesystem?
 The kernel image (e.g. ``vmlinuz``) is provided by the
 ``kernel-image`` package. Image recipes depend on ``kernel-base``. To
 specify whether or not the kernel image is installed in the generated
-root filesystem, override ``RDEPENDS:${KERNEL_PACKAGE_NAME}-base`` to include or not
+root filesystem, override ``RRECOMMENDS:${KERNEL_PACKAGE_NAME}-base`` to include or not
 include "kernel-image". See the
 ":ref:`dev-manual/layers:appending other layers metadata with your layer`"
 section in the