Newsletters are a great way to get non-community members to become actual members. But for some reason we have to instruct them on how to go to stackexchange.com/newsletters, search for Raspberry Pi, and click on the subscribe button. Wouldn't it be better, and possibly increase conversion rates, if we provided a subscribe link from the preview page? That way users can see some of the samplings of what we have to offer before deciding to subscribe.
This feature already exists! Though it's completely undiscoverable at the moment..
Here is a page which you can use to promote your newsletter:
The main newsletter preview page (e.g. here is Stack Overflow's) has a "Subscribe" button at the top now.