Docs: Relabel the "Science" page as Explanation

[benjaoming]

Refs: #9746

This raises two questions:

1. Can we limit the amount of changes to this?
2. Are there any follow-up actions that we can already express or is it better to just plan for a revisit

(The reason that I wanted to minimize this effort, is in anticipation of some sort of separation between what lives on https://about.readthedocs.com/ and what lives in the documentation)

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📚 Documentation previews 📚

• User's documentation (docs): https://docs--9832.org.readthedocs.build/en/9832/

• Developer's documentation (dev): https://dev--9832.org.readthedocs.build/en/9832/

[ericholscher]

I'm not too worried about this one, so I think a move is fine.