add detail related to campaign finance tag format and how used

Why is this change being made?

Updating the /events page to include details related to the Campaign Finance tag process and format.
Provides detailed instruction on who is responsible & what conditions apply to various types of events.

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

/cc @darawarde