Clarifying feature.yml edit is in same MR for Release Post Item

Why is this change being made?

Clarifying that as part of a release post item, features should be added to data/features.yml as part of the same MR. This change was made to the release post template in !40562 (closed) but a subsequent change swapped the block where this was clarified to instead point at this handbook page.

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