[docs] Clarify "About" page about adding new packages

[jesscodez]

It would be helpful if there was more guidance on the About page about the subtleties of adding new packages to Godoc.

Perhaps this is documented elsewhere, and just needs to be linked, but I think it's worth mentioning that you can add a package by doing https://godoc.org/github.com/<PATH>, and that your <PATH> can be your repo root or a subdirectory, as long as it has a doc.go file. It appears not to work otherwise.

^ Perhaps this conclusion is actually incorrect; this was based purely on experimentation and not by looking at source code, so please let me know if I'm wrong!

(For background, this is based on a conversation in the SIG-Docs channel of Kubernetes Slack, about adding docs for the kubernetes/cluster-registry repo)