docs: add Radxa ROCK 5B docs to Single Board Computer section #6309

Job	Run time
default	17m 1s
push	0s
tag	0s
e2e-docker-short	5m 53s
e2e-qemu-short	6m 13s
e2e-iso	2m 5s
integration-aws	0s
integration-aws-nvidia-oss	0s
integration-aws-nvidia-nonfree	0s
integration-cilium	0s
integration-azure	0s
integration-cloud-images	0s
integration-conformance	0s
integration-extensions	0s
integration-gcp	0s
integration-image-factory	0s
integration-image-cache	0s
integration-images	0s
integration-misc-0	0s
integration-misc-1	0s
integration-misc-2	0s
integration-provision-0	0s
integration-misc-3	0s
integration-misc-4	0s
integration-provision-1	0s
integration-provision-2	0s
integration-qemu	0s
integration-qemu-csi-longhorn	0s
integration-qemu-csi-openebs	0s
integration-qemu-encrypted-vip	0s
integration-qemu-csi-rook-ceph	0s
integration-qemu-race	0s
integration-trusted-boot	0s
integration-reproducibility-test	0s
	31m 12s

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