chore: Update "Uploading your Place" docs to point to Open Cloud

[unix-system]

https://rojo.space/docs/v7/getting-started/new-game/

Current guidance:

You'll need an existing game on Roblox.com as well as the. ROBLOSECURITY cookie of an account that has write access to that game.

The new guidance should talk about the latest (and I assume preferred?) Open Cloud guidance - see rojo-rbx/rojo#504 for details. We might want to keep the cookie guidance for legacy support, but it should be made clear from a security perspective that it is not the ideal method and won't work in CI deployments (because cookies reset on IP change).