Feature: Set up a Newsletter subscription

[eryc-cc]

Summary

We can release a newsletter every day, week, or month, based on user options. We can start with a weekly newsletter and build up, if people ask for it.

We can use Substack as the newsletter. Maybe there's a way to automatically queue each post during the week to be sent on a day, eg: Monday 10am, or Friday 10am.

To-do:

• Create a Substack for Viewport
• Check if there's a Zapier integration with Github actions or HugoCMS
• Test submission