x/website: provide redirects from go.dev to pkg.go.dev for popular repository names

[kevinburke]

I tried to find the docs for chamber, a CLI tool, by typing "https://go.dev/github.com/segmentio/chamber" in a web browser. This returns a 404 - the URL I was looking for was "https://pkg.go.dev/github.com/segmentio/chamber".

It would be nice if "https://go.dev/github.com" and e.g. bitbucket, gitlab, other popular domains, redirected to https://pkg.go.dev.

Someone with access to the web analytics should be able to easily verify whether this is a popular mistake or not.

Alternatively, if you don't want to redirect, you could add custom text to the 404 page saying

Did you mean https://pkg.go.dev/(your url)

[dmitshur]

CC @golang/tools-team.

[findleyr]

I think we should avoid partial features, as it leads to confusion and maintenance burden. For example, users getting confused as to why k8s.io modules don't get redirected, and then requesting that we add e.g. k8s.io (or some other popular module prefix) to the list of supported prefixes. Better to keep things simple: pkg.go.dev is the package documentation host.