Update instructions.md with a note (#2612)

* Update instructions.md with a note

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

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

Markdown and style improvement.

Co-authored-by: Derk-Jan Karrenbeld <derk-jan+github@karrenbeld.info>

* [CI] Format code

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Co-authored-by: Derk-Jan Karrenbeld <derk-jan+github@karrenbeld.info>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: 3 people

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

@@ -2,6 +2,11 @@
 
 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
+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.