[Sieve]: Update content.md for Comprehension Approach (#3865)

Added language about the disallowed `%` operator to the Comprehensions approach.

exercises/practice/sieve/.approaches/comprehensions/content.md

@@ -27,7 +27,8 @@ def primes(limit):
             if all(number % divisor != 0 for divisor in range(2, number))]
 ```
 
-This second example using a `list-comprehension` with `all()` is certainly concise and _relatively_ readable, but the performance is again quite poor.
+This second example using a `list-comprehension` with `all()` is certainly concise and _relatively_ readable, but it uses **`%`** (_which the instructions ask you not to use_) and the performance is again quite poor.
+
 
 This is not quite a fully nested loop (_there is a short-circuit when `all()` evaluates to `False`_), but it is by no means "performant".
 In this case, scaling with input size is intermediate between linear and quadratic, so not quite as bad as the first example.