x/website: document how golang.org is deployed

[kevinburke]

Agniva de Sarker and I were trying to figure out how an error in a recent godoc commit made it to golang.org. This required reverse engineering the deployment procedure for golang.org.

The instructions for tip.golang.org are (fairly) clear - there's a cmd/tip binary in the x/tools project with several YAML config files in it.

The instructions for golang.org deployment are less clear. Does it still involve the bash script in the x/tools repository? Which commit is used for deployment? To where is it deployed?

[agnivade]

Relevant issues #25022, #25048. It will be good if there is better clarity on the process for how golang.org gets deployed.