Integrate Mail Chimp with the website

[KadeMorton]

I confirm:

• [x] I've read the contributing guidelines and the code of conduct
• [x] I've checked that this issue applies to this repo
• [x] I've checked the existing issues, no one else has reported this
• [x] I've got a clear and descriptive title

We need to have a way that people can sign up for our newsletter from the website.