[Content] Add Design page to Open Source site

https://opensource.creativecommons.org/ currently lacks any dedicated pages on Design. Through all of the orgs' web properties, we only have one reference to the style guide:

- https://creativecommons.org/2019/10/30/cc-style-guide/

At the very least, we should have a `/design` page on this site including some of the following information:

- Links/embed of the Figma style guide
- General info about Figma (where to download, references for how to use)
- Link to vocabulary
- Credit to Francisco / small bio
- Mention of a11y and the important of access (can cross reference our pages on usability testing: https://opensource.creativecommons.org/contributing-code/usability/)