Explaining supported architectures in snap instructions

The Certbot snap which we plan to make our primary installation method supports the x86_64, ARMv7, and ARMv8 CPU architectures.

According to the [statistics](https://gist.github.com/bmw/7970ee3e3f4c8f8bad8e193a646c6c9b) I pulled from PyPI (which counts Certbot installations using `pip` including those from `certbot-auto`), this covers 97.8% of our user base. I also suspect this situation will get better over time as the older architectures continue to become less popular and supported.

The question I have is how should we approach this issue in Certbot's instruction generator? Should we make a nice glossary/tooltip item about this and explicitly list the supported architectures? I worry a bit about this bogging down the installation process and confusing novice users, most of whom won't have to worry about this, but that probably seems like the best approach to me personally.