Clarify release post instructions on performance improvements and bug fixes

Why is this change being made?

During the 12.10 milestone release post cycle, we found that some information was lacking around how to report performance improvements and bug fixes. This MR attempts to add more information to those topics for future release post organization.

How will this merge request impact page speed?

This will impact the page speed only negligibly.

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