doc: Document rcutree.nocb_nobypass_lim_per_jiffy kernel parameter

This commit provides documentation for the kernel parameter controlling
RCU's handling of callback floods on offloaded (rcu_nocbs) CPUs.
This parameter might be obscure, but it is always there when you need it.

Reported-by: Frederic Weisbecker <frederic@kernel.org>
Reported-by: Uladzislau Rezki <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>