fix: duplicate email icon in website footer

[A-d-i-t-y]

What happened

The website footer (https://pipecd.dev) displays two identical email
icons both pointing to pipecd.dev@gmail.com. This appears to be a
duplicate entry across the developer and user link sections in
the site configuration.

Screenshot

Expected behavior

Only one email icon should be displayed in the footer.

How to reproduce

1. Visit https://pipecd.dev
2. Scroll to the footer
3. Two email icons are visible side by side

Suggested fix

Remove the duplicate email entry from either the developer or
user section in docs/config.toml

[rahulshendre]

Hey @A-d-i-t-y,
These are intentional and represent two different mailing lists, Developer Mailing List and User Mailing List.
We don't have active mailing lists yet, so both currently point to the same email address - ref slack thread

Closing for now.