Update PTO Ninja - holidays

Why is this change being made?

PTO Ninja does not automatically create an OOO event when holidays are added. Though this feature might change soon, the handbook should reflect the current features. See this comment confirming that an OOO event is not auto-created. Updating this will allow employees to understand from the handbook how PTO Ninja should operate when adding holidays.

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