Release runbook in Delivery team handbook

Why is this change being made?

Part of gitlab-org/release/docs!202 (merged), includes information for the delivery team, allowing the team to find the runbook quickly in an urgent situation.

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what