The default value was changed from `registerWhenStable` to
`registerWhenStable:30000` in 29e8a64cf02fa9b80d38c30091e0b730403c54c8,
but the decumentation was not updated to reflect that.
This commit updates the documentation to mention the correct default
value.
PR Close#37555
The docs don't mention that the app will never be stable if a `setInterval` is running somewhere, and that it will prevent the servcie worker to be registered too.
PR Close#28102