7-day welcome series for new users

Build in public day 17/30: In finished writing and setting up the welcome series for new users. With new habit formation the first major milestone is to make it to a 7-day streak, so that's the goal of the email series 🔥

I look forward to seeing how completion/engagement with the welcome series correlates with retention and successful habits long-term. I'll have stats to share later.

I can't attach them all here, so here's the tweet that includes them.