pidigits example website is gone

super-computing.org now redirects to https://datascienceparichay.com/super-computing/ which seems a bit sketchy. Let's find another source for the pi digits dataset.

Inspect the pidigits example to locate its reference to super-computing.org, then verify a trustworthy replacement source for the pi digits dataset. Done means the example no longer points to the unavailable website and the replacement dataset is suitable for the example.

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