Adding Sustainability to the Staff Handbook

[KirstyPringle]

As part of the Application to Green DiSC (Bronze) we are reviewing our sustainability policies.

Two questions for @selina-aragon

Could we:

1. Add a page on sustainability to the staff handbook: https://docs.google.com/document/d/1bnqZhHtU3LqxS5H6iyujw4pQbVDW9P6ax0zS1R60yE8/edit?tab=t.0 (still in draft!)

2. Add a checkbox to the onboarding page to point people toward the policy and have a discussion on sustainability?