Remember you can run a local server with all your locally-installed packages and exactly the correct version of the core Go packages with:

    godoc -http=127.0.0.1:9000 &

(or local OS equivalent), which make them available at http://localhost:9000.

Godoc is more useful for the searching for packages you do not currently have than the docs themselves, because you ought to be running a local server. (I have noticed if you add new packages the server will need to be restarted, but it picks up on changes to existing packages as you change them.)