Add a link to dashboard showing tier to tier product change from the pricing model page in the handbook index.html.md

Why is this change being made?

We are making this change to provide visibility into what the conversion rate of customers moving from tier to tier is. This supports the fifth paragraph under the Hybrid sales model section.

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