My guess is that many ATProto users are enthusiasts of decentralization and some of them (like me o/) might have migrated some stuff to Codeberg too. This PR allows us to read README.md from Codeberg (as well as from GitHub, GitLab and Tangled that were already there!)
For example, a repo like https://codeberg.org/Codeberg/Contributing and branch wiki-notice should resolve to https://codeberg.org/Codeberg/Contributing/raw/branch/wiki-notice/README.md.
Looks good.
Just a note, the semi-secret way to handle any url is to update your labels/annotations with io.atcr.readme= https://tangled.org/evan.jarrett.net/at-container-registry/blob/main/Dockerfile.appview#L41-42