Update source/handbook/marketing/events/index.html.md

Why is this change being made?

Clarity on customer references and events - how we support the process

Describe in detail answer to question on why this change is being proposed, in accordance with our value of Transparency

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Does this MR meet the acceptance criteria?

Conformity

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