Add note to Transparency value about how to update public vs non-public

Why is this change being made?

It seems sometimes that folks forget that the handbook is a living document and that we can continually update it, even the sections that seem like they should be immutable. This MR puts a call out specifically under transparency about how people should make an MR if they think something should be changed about whether something is public or not.

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