Add icon for Codeberg social link

[andrefelipeos]

Currently, Minima does not support adding a Codeberg icon/social link.

Codeberg is "a collaboration platform providing Git hosting and services for free and open source software, content and projects". They provide a logo-kit here, under the Creative Commons CC0 license.

[mattr-]

Jekyll's maintainers aren't likely to add more icons/social links on their own, since we don't use 90% of them. If you want a social link for Codeberg, the most effective way is to open a pull request to add one so that we can review and merge it. Thanks!

[antoineco]

This was addressed in #788