Documentation: RISC-V: patch-acceptance: mention patchwork's role

Palmer suggested at some point, not sure if it was in one of the
weekly linux-riscv syncs, or a conversation at FOSDEM, that we
should document the role of the automation running on our patchwork
instance plays in patch acceptance.

Add a short note to the patch-acceptance document to that end.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
Link: https://lore.kernel.org/r/20230606-rehab-monsoon-12c17bbe08e3@wendy


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>