Re-enable documentation on the TabPFN website

[brendan-priorlabs]

Describe the issue linked to the documentation

We used to have documentation for the TabPFN package on our website. Some users have requested we restore that. See, e.g., this report on Discord.

Suggest a potential alternative/fix

Generate and push documentation to the site as part of the release process. We could then make sure it's properly versioned too. Ideally we would automate this too.

[brendan-priorlabs]

Assigning @noahho for putting some notes in our release process.