test-reduce-basics instructions are not clear

[astronaut-wannabe]

(define-test test-reduce-basics
    "The reduce function applies uses a supplied
     binary function to combine the elements of a
     list from left to right."
  (assert-equal ___  (reduce #'+ '(1 2 3 4)))
  (assert-equal ___ (reduce #'expt '(2 3 2))))

This doc string doesn't really make sense, specifically the "function applies uses a" bit.

I was going to open a PR, but I am not actually sure what it is supposed to be. Maybe:

The reduce function combines the elements of a list, from left to right, by applying a supplied binary function to the list elements

[bileschi]

I guess that's a bit easier to understand. Maybe drop the 'supplied'? Feel free to make a PR.

[rowanthorpe]

If the merged commit fixed this adequately it would be good to close the issue, otherwise to add info about what is still needed.

[Slids]

Since there's been no update in a few years, I'm guessing the fix was adequate.