Feature Proposal: Improve text for linking other fediverse handles

Is your feature request related to a problem? Please describe.

User settings have a section for "External accounts" where we are faced with two options:

1. Sign in with orcid
2. Specify the @username@domain.com of the account, or paste a URL

Number 1 is quite clear, but I didn't understand what we were expected to do with number two until I saw that other users had their other fediverse accounts displayed on their profile, and I joined the dots. I added my mastodon and pixelfed handles, and they are both displayed on my profile with their avatars.

Describe the solution you'd like I would like a better text/label that explained:

1. Why do we want to do that / the effects of doing it (e.g. "Signing in with orcid will populate your profile with the following data: last publication, current and past institutions, research themes and publication types", "Adding other accounts using ActivityPub will display your federated handles and avatars in your profile")
2. Detailing the scope of 2, explaining if any software that uses ActivityPub is accepted or just a subset, or actually anything.

Describe alternatives you've considered

<img width="656" height="238" alt="Image" src="https://github.com/user-attachments/assets/240393ef-85fe-4c66-a17a-2250f13aff2a" />

Additional context Explanation here: https://sandbox.openscience.network/pub/objects/01K895QRNB00TBAXHFFB3VEGQV