UG: Advise Mac users to install a specific JDK

AB3's use JavaFX is known to cause compatibility issues with most Mac
JDK distributions. In particular, it can cause the UI to show
garbled text due to font issues.

Let's advise Mac users to use a specific JDK that has built-in JavaFX
support and has been verified not to cause the aforementioned
compatibility issues.

docs/UserGuide.md

@@ -12,7 +12,8 @@ AddressBook Level 3 (AB3) is a **desktop app for managing contacts, optimized fo
 
 ## Quick start
 
-1. Ensure you have Java `17` or above installed in your Computer.
+1. Ensure you have Java `17` or above installed in your Computer.<br>
+   **Mac users:** Ensure you have the precise JDK version prescribed [here](https://se-education.org/guides/tutorials/javaInstallationMac.html).
 
 1. Download the latest `.jar` file from [here](https://github.com/se-edu/addressbook-level3/releases).