Clarify UpdateCheckData usage to prevent errors

UpdateCheckData has odd behavior in certain scenarios, so I clarified how to avoid potential issues. First, avoid a YAML formatting issue by using single quotes (') if your UpdateCheckData starts with |. Second, explain that RegEx pipe operators (|) don't work, since we also use | to separate each field within UpdateCheckData. Maybe a YAML list should be used instead, but that's an extremely low priority