Accessibility docs updates

[Izzy-Snyder]

Unrelated to an open issue, I have specific approval to work without an open issue from @raclim as part of the Open Source Internship.

Changes:

• updated the accessibility docs to include color related accessibility guidelines and more resources. Added a disclaimer and adjusted the formatting to cover multiple areas of accessibility.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123

[raclim]

Sorry for the delay on this (It's been a bit hectic but should be able to give a closer look at this by early next week)!

Also wanted to update that I think it'd be cool if you'd also like to add a URL to the Contrast Palette Checker you created to the Contributor Docs! Do you think that might be something you're down with or would make sense here?