Update instructions.md with a note

Added note to clarify "ratePerHour" and "dayRate" meaning.

Author: Erz3

exercises/concept/freelancer-rates/.docs/instructions.md

@@ -2,6 +2,10 @@
 
 In this exercise you will be writing code to help a freelancer communicate with their clients about the prices of certain projects. You will write a few utility functions to quickly calculate the costs for the clients.
 
+~~~~exercism/note
+In the next tasks, the ==ratePerHour== variable and the ==dayRate== function are related to money. The units of measurement are money for a unit of time (hours and days respectively).
+~~~~
+
 ## 1. Calculate the day rate given an hourly rate
 
 A client contacts the freelancer to enquire about their rates.