Email sign-up capability

[CorinnaPhillips]

Can an option for site visitors be provided to sign-up to my email list.
It would be good to have this on the top nav which stays present as you scroll down the page. If this is not possible then either on the very top black nav or at the top of the sidebar.

Depending on which option is selected I will need to create a corresponding form to use in Convertkit - potentially we will need to put custom CSS into convertkit for this form.

[CorinnaPhillips]

See associated Trello card: https://trello.com/c/qJP3bceD/16-see-if-its-possible-to-put-email-list-sign-up-in-the-very-top-black-bar-before-the-email-address