Improve documentation webpage

[tomicapretto]

• Brings back the Getting Started section to the webpage
  • Rerun this notebook
  • Add watermark
  • Replaces Aesara with PyTensor
  • Move the families table to a better location
  • Bring back the tip callout.
  • Maybe something else too, I just don't remember all the minor changes.

[review-notebook-app[bot]]

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