Update ChildWorkflowOptions comment to indicate the default WorkflowIDReusePolicy and WorkflowIdConflictPolicy

[codemonkeycxy]

Is your feature request related to a problem? Please describe. Currently, it's not clear what the default WorkflowIDReusePolicy and WorkflowIdConflictPolicy are by reading the SDK code https://github.com/temporalio/sdk-go/blob/master/internal/workflow.go#L390-L392

Describe the solution you'd like Add inline comments to make the default behavior clear

Describe alternatives you've considered Document it in the Temporal developer guide https://docs.temporal.io/develop/go

Additional context N/A

[Sushisource]

@codemonkeycxy Would you be willing to just make a PR for this?