Follow experience could be improved for better adoption
Is your feature request related to a problem? Please describe
I believe it is hard for the moment to understand how to follow an episode. It only says "your username" assuming everybody understand you need an activitypub account somewhere to subscribe.
Describe the solution you'd like
A bit more explanation telling you need an activitypub account and some helpful hint like "what is it?" or "why it's cool" would surely help.
Also, given the general mainstream usage of such platforms, I wouldn't be surprise that one looking to follow but who has no account might look for a way to sign up somewhere. This is really new and still very niche (but promising!) to adapt to the idea that you could follow something on a website while using an account coming from another platform (unless it's your facebook or google account.. sigh) So that may be good to think of a scenario of someone looking to "sign up" somewhere. How could that be answered?
A complementary idea would be to add a hint in the spirit of "Don't worry, there are many other ways to not miss our next episodes" linking to rss link and other platforms would be great to avoid letting people without such account lost. (and these are most of the people in full objectivity).
Additional context
Overall UX of Castopod is just amazing! Keep it up. It's one the few rare things which I believe need a bit more love :)