Yeah, we'll work to improve the documentation on this.
Though.. note that WhatsApp doesn't have any documentation on their key discovery either, because WhatsApp is not a federated system. Achieving automatic end-to-end encryption in a federated system, when it wasn't there before, isn't so easy. So there's bound to be some growing pains, but we're still trying :)
Are you with Proton? Maybe the documentation you need is just a lock on the sent email that says "Used key for <email> from keys.openpgp.org", and the recipient could also have a cleartext message saying "Encrypted with key for <email> from keys.openpgp.org"?
Though.. note that WhatsApp doesn't have any documentation on their key discovery either, because WhatsApp is not a federated system. Achieving automatic end-to-end encryption in a federated system, when it wasn't there before, isn't so easy. So there's bound to be some growing pains, but we're still trying :)