I would go here:
Create an account, then click “Submit a request”, and for the Category select “Node Provider → Prospective Node Providers → Information Request”, and fill out the rest of the form.
I don’t know if this website is “official” yet, but it’s working well, so why wait for full documentation for someone who wants to get the ball rolling now?
As an aside, I’m sure a lot of us signed up ages ago to get notified about being a node provider. That notification never came. I suppose it still could, but DFINITY is obviously not making an effort to get the community into the data center game. Understandable, since there is a high barrier to entry, but still kind if disappointing, since the perception of decentralization in the crypto community would be much higher if average Joes were running nodes in data centers around the world. From what Dom has said, there’s actually a pretty good level of decentralization with the existing node providers that have signed up, but it’s not currently perceived that way on Twitter, Reddit, etc.