Add subscribe form to homepage

I want to get rid of the mailchimp-hosted page. For one, I can't even have a favicon.

I'll need a mailchimp form "component".

The form is hidden within.

Also need to reference and update the docs here:
- https://stackoverflow.com/questions/21526408/mailchimp-subscribe-using-jquery-ajax

References:
- https://mailchimp.com/help/host-your-own-signup-forms/

Locate the homepage and the commented Mailchimp form shown in the issue, then read the linked Mailchimp and Stack Overflow references before deciding how the existing markup is intended to be integrated. Done means the homepage contains a usable subscribe form instead of sending visitors to the hosted page, and the related documentation references are updated.

Written by the indexing model from the issue text.