rhel_kernel_workflow.adoc: Submitting large changeset guidance
MR centos-stream-9 !41 (merged) [1] resulted in 130 reviewers being added to the MR
by the webhooks. While this isn't generally going to be a problem, a
reminder to separate out large changesets can't hurt anything.
Add a suggestion about submitting large changesets, and reference the
upstream docs.
[1] centos-stream-9!41 (merged)
Signed-off-by: Prarit Bhargava prarit@redhat.com