Add statement about due date vs SLA discrepancy

Why is this change being made?

A question came up in Slack about the discrepancy between the SLA and the due date on issues

During a recent meeting, there was confusion about security issue due dates. (e.g Example) There is a issue due date AND then there is the date that the security issue breaches the SLA. In some instances, these dates are not aligned. Is there a handbook that explains the difference between the two?

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