Add new utility/info pages

I think we should add a few new pages to the site for the redesign.

Inspired by It’s Beginning to Look a Lot Like XSSmas/snyk's SECURITY.md. We're a static site, but I still think proactively it'd be a good thing to have.

Checklist of desired pages:

• An accessibility statement
• A security and privacy statement
• A D&I timeline
• A "write for us" page, including linking to the writing styleguide
• A team page