Document that valuation can be called

[user202729]

I think it's not too easy to find .valuation(2) i.e. .count_trailing_bits() as is.

e.g. online search result for "SageMath integer valuation" gives that page as one of the top results. Or maybe https://doc.sagemath.org/html/en/reference/valuations/sage/rings/valuation/valuation.html

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