Add documentation for long-running when using JupyterLab OnDemand

• From #help-desk thread: https://unity-user-community.slack.com/archives/C04VBHU8QQN/p1699402284273519
• User asked how to avoid the kernel being interrupted when their computer is disconnected from the internet while using JuptyerLab OnDemand
• Add documentation on how to run something long-running