Feature Request: doc on how to create chaos that runs forever (w/o scheduler)

[Yiyiyimu]

Chaos Mesh dashboard provides methods to define chaos runs forever, and the same case could be found in e2e test for podchaos.
But following the way of podchaos test, it could not work and report error spec.scheduler: Invalid value: "null": schedule should be omitted

I think it would be better if it could be written in the doc.