If you want to logically split an iterator after `n` items, you might first
discover `take`. Before this change, you'd find that `take` consumes the
iterator, and you'd probably be stuck. The answer involves `by_ref`, but that's
hard to discover, especially since `by_ref` is a bit abstract and `Iterator`
has many methods.
After this change, you'd see the example showing `take` along with `by_ref`,
which allows you to continue using the rest of the iterator. `by_ref` had a
good example involving `take` already, so this change just duplicates that
existing example under `take`.
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