[docs] Comments on potential srun orders during Slurm Deployment (#8183)

doc/source/deploying-on-slurm.rst

@@ -32,11 +32,15 @@ Clusters managed by Slurm may require that Ray is initialized as a part of the s
 
   srun --nodes=1 --ntasks=1 -w $node1 ray start --block --head --redis-port=6379 --redis-password=$redis_password & # Starting the head
   sleep 5
+  # Make sure the head successfully starts before any worker does, otherwise
+  # the worker will not be able to connect to redis. In case of longer delay, 
+  # adjust the sleeptime above to ensure proper order.
 
   for ((  i=1; i<=$worker_num; i++ ))
   do
     node2=${nodes_array[$i]}
     srun --nodes=1 --ntasks=1 -w $node2 ray start --block --address=$ip_head --redis-password=$redis_password & # Starting the workers
+    # Flag --block will keep ray process alive on each compute node.
     sleep 5
   done