clarify instructions

Author: Liam310

Sprint-3/4-stretch/README.md

@@ -4,6 +4,6 @@ These stretch activities are not mandatory, but we hope you will explore them af
 
 In this exercise, you'll need to **play computer** with the function `find`. This function makes use of while loop statement. Your task will be to step through the code to figure out what is happening when the computer executes the code.
 
-Next, try implementing the functions specified in `password-validator.js`.
+Next, try implementing the function in `password-validator.js` (description of its expected behaviour is in the accompanying `password-validator.test.js` file).
 
 Finally, set up your own script and test files for `card-validator.md`