The `pkg` package is a horrible convention. Having a `cmd` directory makes sense, as each binary needs to be a separate package, but putting all your libraries under a `pkg` directory is unneeded.
The word "lib" makes more sense. But, also, its unnecessary.
Comingling non-Go dirs with Go code makes it hard to navigate, since some dirs will be Go packages, and some won't. You may want to have documentation (/docs, perhaps), test data (/test?), build output dirs (/build or /dist), Docker/Kubernetes/Helm dirs (/docker, /k8s, etc.), Protobuf files (/proto), and so on, usually all in the root of the project.
Secondly, these directories might conflict with Go package names. We have a project that has a package called "documents", which is about persistent documents, which we'd have preferred to call "docs", but the root already had a /docs folder for actual documentation.
Personally, I prefer "src".
More fundamentally, it feels a bit screwy for a multi-faceted 'project' to live wholly inside $GOPATH in the first place. But at the same time, it's natural.