Add high level onboarding to Figma file: "Start Here"

[lklyne]

Goal: make it easier for designers and developers to understand the figma file

• Add start here page
• How to use the file
• Links to the relevant repositories
• Atomic structure?

Inspiration: https://www.figma.com/file/eWS5hlR2VgMSiEl5H10ujz/HDS-Library?type=design&node-id=2896%3A3&mode=design&t=nRduTiPLwecDF71Q-1