Document the need to delay starting up of Stargate after shutdown

[jmon-ds]

When restarting Stargate using the starctl script, if we shutdown and start Stargate with the script right away within a second, we get the error

Exception (java.lang.RuntimeException) encountered during startup: A node with address /10.16.37.43 already exists, cancelling join. Use cassandra.replace_address if you want to replace this node.

ERROR [DSE main thread] 2021-10-21 17:47:22,384 CassandraDaemon.java:821 - Exception encountered during startup

java.lang.RuntimeException: A node with address /10.16.37.43 already exists, cancelling join. Use cassandra.replace_address if you want to replace this node.

We need to document a delay of 30 seconds between shutdown and subsequent start up to avoid the Gossip issue.